Previously the groups service used the first HTTP(S) URL returned by
`store.searchUris()` to get the URL used to search for associated groups. In
practice, the URIs from the main frame always appeared first in this
list, and the main URL from that frame was the first entry within that sublist.
However, the `store.searchUris` function doesn't provide any guarantee of this
and future changes could break this invariant.

This commit adds a `store.mainFrame()` function which returns the main
frame, the one with no `id`, and modifies the groups service to use the
main URI for that frame.

A change in behavior here is that if the top-level frame was a non-HTTPS
frame but embedded an HTTPS frame, then the group search would have used
the URL from the HTTPS frame. Now it will use the non-HTTPS URL from the
top-level frame.

Separate hover areas for main action and submenu toggle

Merge in changes from https://github.com/hypothesis/client/pull/1188

Menu usability improvements

Bump dompurify from 1.0.10 to 1.0.11

Bump preact from 10.0.0-beta.2 to 10.0.0-beta.3

Bump focus-visible from 5.0.0 to 5.0.1

For menu items that have associated submenus, make it clearer that there
are two separate click zones by highlighting only the clickable area for
the main action when hovering that part of the item.

For menu items without submenus, there should be no visual change.

The implementation adds a `.menu-item__action` element that wraps the
content of the menu item excluding the submenu toggle.

The CSS has been re-organized to group together all of the rules that
affect a specific element. This makes it easier to verify that there are
no states which visually conflict for a particular element.

Bump eslint-plugin-react from 7.13.0 to 7.14.1

Refactor clearSelection out of sidebar-content and into the store

Bumps [preact](https://github.com/developit/preact) from 10.0.0-beta.2 to 10.0.0-beta.3.
- [Release notes](https://github.com/developit/preact/releases)
- [Commits](https://github.com/developit/preact/compare/10.0.0-beta.2...10.0.0-beta.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.13.0 to 7.14.1.
- [Release notes](https://github.com/yannickcr/eslint-plugin-react/releases)
- [Changelog](https://github.com/yannickcr/eslint-plugin-react/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yannickcr/eslint-plugin-react/compare/v7.13.0...v7.14.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [focus-visible](https://github.com/WICG/focus-visible) from 5.0.0 to 5.0.1.
- [Release notes](https://github.com/WICG/focus-visible/releases)
- [Commits](https://github.com/WICG/focus-visible/compare/v5.0.0...v5.0.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [dompurify](https://github.com/cure53/DOMPurify) from 1.0.10 to 1.0.11.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](https://github.com/cure53/DOMPurify/compare/1.0.10...1.0.11)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Use clearSelection from the store instead of from sidebar-content.

- This clears the selected annotations, groups, direct-linked
  group error, and resets the selected tab to annotations if it's
  currently set to orphans.
- Change the action of clearSelectedAnnotations to CLEAR_SELECTED_ANNOTATIONS
  so CLEAR_SELECTION can be used as the action for clearSelection.
- Add tests in index-test over the global store since this triggers an
  action in multiple store modules.

Click and mousedown events on a menu are no longer propagated upwards.
Therefore the `document.body`-level event listeners that cause a menu to
close when clicking outside of the menu need to use capture rather than
bubble-phase listeners.

 - Do not close the menu if the user presses the mouse in the lower
   right corner of the toggle button _just_ where the notch/arrow at the
   top of the menu content appears
 - Do now show outline when pressing mouse down on a menu item. An
   outline will still be shown if the menu has keyboard focus
 - Close menu when an item is activated with Enter or Space keys

Add "Copy link" action to groups menu

Feedback on the first iteration was that "Copy link" was ambiguous. Add
the term "invite" or "activity" to the label to indicate what the link
is for, depending on whether it is a group that the user can join or
not.

Replace references to old groups menu styles in new component

Update icon for "New private group" menu item

Update to latest icon from https://hypothicons.netlify.com.

Add an action to provide a convenient way to copy the sharing link
directly from the groups menu.

Depending on whether the group is private or open and whether the
receiving user is a member or not, the link may present the user with a
Join page or the activity page for the group. To simplify the client logic, the
text just says "Copy link".

I evaluated popular npm packages for this purpose (eg. [1]) but encountered
issues where they were not transpiled for use in older browsers or
included workarounds for browsers we no longer support (eg. IE 9).

If we do decide to use an existing package in future, we can keep this
utility module as a wrapper around it.

[1] https://github.com/sindresorhus/copy-text-to-clipboard

This replaces some references to the styles for the old groups menu in
the new implementation. The menu label is now slightly darker as it
uses the same grey as the menu items. Otherwise there should be no
noticeable visual changes.

The CSS itself has been simplified compared to the previous
implementation.

Update group menu styles

This enables consumers to use `&&` or `||` conditionals to compute the
`icon` prop.

Convert `<search-input>` component to Preact

 - {show, hide} => {renders, doesn't render} to clarify that we're
   checking whether an element is rendered at all, as opposed to merely
   visually hidden
 - Replace ambiguous GitHub issue reference with URL

This makes it easier to see when a submenu item is hovered.

 - Use the string "blank" instead of `null` as a more explicit indicator
   that a menu item should show a blank space for an icon
 - Rename two variables to indicate their boolean-ness

The icon is from the Hypothicons set at https://hypothicons.netlify.com