Introduce `xs` text size and update `text-sm` to `text-xs` in components

Add `xs` as a new text size equal to the existing `sm` text size and
update components using `text-sm` to use `text-xs`.

This will allow us to change the `sm` size to be the same as the `base`
size.

src/sidebar/components/Annotation/AnnotationLicense.tsx

@@ -9,7 +9,7 @@ import {
  */
 export default function AnnotationLicense() {
   return (
-    <div className="pt-2 border-t text-sm leading-none">
+    <div className="pt-2 border-t text-xs leading-none">
       <Link
         classes="flex items-center"
         color="text-light"

src/sidebar/components/Annotation/AnnotationShareControl.tsx

@@ -158,7 +158,7 @@ function AnnotationShareControl({
               className={classnames(
                 // Slightly larger font size for touch devices to correspond with
                 // larger button and input sizes
-                'flex w-full text-sm touch:text-base'
+                'flex w-full text-xs touch:text-base'
               )}
             >
               <InputGroup>

src/sidebar/components/Annotation/AnnotationTimestamps.tsx

@@ -80,7 +80,7 @@ export default function AnnotationTimestamps({
     <div>
       {withEditedTimestamp && (
         <span
-          className="text-color-text-light text-sm italic"
+          className="text-color-text-light text-xs italic"
           data-testid="timestamp-edited"
           title={updated.absolute}
         >

tailwind.config.mjs

@@ -81,6 +81,7 @@ export default {
         // This is a collection of font sizes used in existing sidebar components,
         // which will grow during the conversion-to-Tailwind process. These
         // are descriptive, not aspirational or prescriptive.
+        xs: ['11px', '1.4'],
         sm: ['11px', '1.4'],
         base: ['13px', '1.4'], // Current base font size for sidebar
         md: ['14px'],