Bump minSdk to 24 due to a serialization bug

We are relying heavily on the kotlinx.serialization library. Many dependencies also use it indirectly, so forcing an older version is no longer feasible. Newer versions use CharsetDecoderICU which had a bug in Android <= 23. The team decided that instead of workarounds, we just bump minSdk to 24 and require at least Android 7 for new releases.

See https://github.com/Kotlin/kotlinx.serialization/issues/2231

Closes #3073 (closed)