Script origin lookup used `document.currentScript` which does not work
for module scripts. Use `import.meta.url` instead which does [1].

This change will result in the `allowUrls` Sentry configuration being
set once again, which will hopefully prevent some reports from external code (eg.
browser extensions) from being sent to Sentry.

Fixes https://github.com/hypothesis/client/issues/4046

[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import.meta