Bump docs and compatibility checking for API Level 24.
Also, remove a SubjectTest workaround that became unnecessary not because of that bump but because of https://github.com/google/truth/commit/68d13aaddeb2bc29850fb13cba4654bf20197f22. (It involves StringBuilder, which doesn’t become Comparable until Android14 / API Level 34 (before, after).)
This minSdkVersion bump follows other Google foundational libraries, and we expect the bump itself to have no practical impact on users.
RELNOTES=Our Android minSdkVersion is now 24 (Nougat). This follows the minimum of Google’s foundational Android libraries, and we expect it to have no practical impact on users.
PiperOrigin-RevId: 953631364