Update env components to these versions:
- Python 3.9
- Pin NDK to 21.4.7075529 as done by Godot
Not updating Android API level to 30 yet as some feature work is needed in
Godot to support new requirements.
Mono 6.12.0.144 is still a Preview release, but contrarily to 6.12.0.122,
it has a successful Windows build. It also theoretically finalizes support
for Apple M1, so we can attempt using it to build Mono for that arch.
Upgrades us to the current stable release.
Further work is done in Preview on Apple Silicon support but we'll look into this
after the Godot 3.3 release.
Following up on #22, we should target API level 18 like the Godot source does,
which is used by armv7/x86 builds. 64-bit builds do require API level 21 as a
minimum, but our build scripts handle upgrading this value already.
