doc: fix link to android api level support

[erisu]

Motivation and Context

Links to the Android API Support Level was incorrect.

Description

Update the link and extracted it to be defined in a single location.

Testing

Tested link local with npm run serve

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary