feat: Support API 21

[BenjaminHalko]

Adds support for API 21, the oldest API supported by Compose.

TODO:

• [ ] Notifications requires API 26
• [ ] StandardCopyOption.REPLACE_EXISTING requires API 26
• [x] setInstallReason requires API 26
• [ ] CompactDecimalFormat requires API 24
• [ ] connectivityManager.activeNetwork requires API 23
• [x] app.checkSelfPermission requires API 23
• [x] pm.isIgnoringBatteryOptimizations requires API 23
• [ ] Patches don't seem to load correctly on anything lower than API 26

[BenjaminHalko]

Currently it will launch on API 23, but anything below that crashes on startup.

[BenjaminHalko]

I don't think it is worth it to support this low, so I am closing this.