Clarify the different ways that "matches patterns" are used

[dotproto]

Derived from a comment by @dotproto in #36069 (review)

While reviewing PR #36069 I realized that my feedback was focused on how match patterns are used for (optional) host permissions declarations in the extension manifest. Unfortunately, that's just one of several ways that match patterns are used in extensions.

This is a non-exhaustive list of WebExtensions API surfaces that use match patterns. At the moment the exact differences between how these various surfaces use match patterns is unclear.

1. host permissions declared in the host_permissions and optional_host_permissions manifest fields.

   • same usage pattern should apply to the origins field of the object passed to permissions.request()

2. the matches field of content script declarations

   • should also apply to the matches field in the object passed to scripting.registerContentScripts()
   • should also match the matches field in the object passed to userScripts.register()

3. the matches as used in entries of the web_accessible_resources manifest field (MV3 only).

4. In the hide_matches and show_matches fields of the page_action manifest field.

5. the url field of the webRequest.RequestFilter object.

6. the url field of the filter object passed to tabs.onUpdated().

7. the url field of the options argument passed to tabs.query()

8. the matches field of the generic UrlFilter object.

This list is non-exhaustive. I should go through searchfox.org and cs.chromium.org to look for additional uses I may have missed.