[sensors_plus] Migrate Android part to Kotlin

[vbuberen]

Description

One more PR to migrate Android parts of Plus plugins to Kotlin, like #666.

As previous time I tried to not change the behavior as much as I could. Everything works in a same way as it worked before.

Additionally, I've updated the README to fix Flutter favorites image and add build status for sensors_plus workflow.

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[miquelbeltran]

Looks good!