[local_auth] Add option to AuthenticationOptions to force strong biometrics only.

[BeMacized]

This PR adds a strongBiometricsOnly flag to the AuthenticationOptions on Android, to enable authenticating with strong biometrics only.

Note: I have tested this on a device with strong biometrics present. While the appropriate error responses should be returned on a device with only weak biometrics, I have not been able to test this as I have not yet found any hardware that meets this criteria.

~~This PR still lacks tests and pubspec/changelog updates, I'll take care of this tomorrow.~~

Relevant issue:

• flutter/flutter#81169

Pre-launch Checklist

• [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• [x] I read and followed the [relevant style guides] and ran [the auto-formatter]. (Unlike the flutter/flutter repo, the flutter/plugins repo does use dart format.)
• [x] I signed the [CLA].
• [x] The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• [x] I listed at least one issue that this PR fixes in the description above.
• [x] I updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy], or this PR is [exempt from version changes].
• [x] I updated CHANGELOG.md to add a description of the change, [following repository CHANGELOG style].
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] I added new tests to check the change I am making, or this PR is [test-exempt].
• [x] All existing and new tests are passing.

[jcho0216]

@BeMacized When do u think that this job could be done? I want to use this feature in my projects asap :)

[GaryQian]

@BeMacized Whenever you get a chance, rebase this PR and we can start to take a look at reviewing

[Hixie]

@BeMacized Is this PR still on your radar?

[reidbaker]

Closing this as stale and there are conflicts. Please re-open if progress can be made.