[WebAPI] Web Share: Implement canShare() method

[Rumyra]

Acceptance Criteria

• The listed features are documented sufficiently on MDN
• BCD is updated
• Interactive example and data repos are updated if appropriate
• The content has been reviewed as needed

For folks helping with Firefox related documentation

• Set bugs to dev-doc-complete
• Add entry to Firefox release notes if feature is enabled in release
  or
• Add entry to Firefox experimental features page if feature is not yet enabled in release

Features to document

[Web Share] Implement canShare() method

Related Gecko bugs

https://bugzilla.mozilla.org/show_bug.cgi?id=1666203

[hamishwillee]

This IS a release because, even though the web share API is behind a preference, it is enabled on Android by default. So a case where we need to update both experimental features and release notes.

Fortunately I did most of the work for Navigator.canShare() in #8381.

• BCD Update: Firefox 96 supports Navigator.canShare() browser-compat-data#13810
• Release note: Not required, assuming this is behind a preference (confirming, but pretty sure)
• Experimental features
  - had a note this was not supported. Removed - Remove Experimental Features note about about canShare() support #10876
  - did not reflect that API enabled on Android. Fixed Ff96 canShare release note AND experimental features #10933
• Release note (for android) - Ff96 canShare release note AND experimental features #10933
• dev-doc-complete

This is pretty much done once everything merges.

[Rumyra]

Going to close in light that BCD will eventually be merged - I can check at the end of the project 👍