Update minimum API level

[mhsmith]

When deciding whether to desupport old API levels, use the Google Play statistics from the Android Studio new project wizard. The code which downloads the data is at tools/adt/idea/android/src/com/android/tools/idea/stats/DistributionService.java, and the URL it downloads is https://dl.google.com/android/studio/metadata/distributions.json. However, this has been updated irregularly in the past.

Checklist in product/README.md.

Relevant changes:

• 23:
  • Dynamic linker improvements. This will allow many workarounds to be removed from the importer.
  • TestAndroidOutput fails to read logcat on ARM64 emulator, API levels 21-22 #771
• 24:
  • Dynamic linker DT_RUNPATH support (see above link)
  • Large file support on 32-bit platforms. This should allow us to remove target/python/patches/lfs.patch.

[mhsmith]

distributions.json (with a Last-Modified header of 02 Jun 2023), now shows API level 23 with 97.5% support, so we can move to that now.

Not only does this allow removing the workarounds in the importer, it also allows removing a build-time patch (#980).

Note that as of Chaquopy 15.0, we have a serious bug that's specific to API level 23 (#1139).