## Description:
Refactor gradle build files to use Kotlin DSL instead of Groovy.
There were also a bash script and a python script that needed to be
updated because they relied on parsing the `build.gradle` files written
in Groovy.
This PR completes the work started in:
https://github.com/syncthing/syncthing-android/pull/2000
The upgraded compile SDK requires an upgrade of gradle, which introduces a
build error with api lvl <21:
> Error while processing [...]/app/src/main/res/drawable/ic_close_24dp.xml :
Invalid color value ?attr/colorControlNormal
Explanation: https://stackoverflow.com/a/49501629
Also minor NDK update
* Updated Syncthing to v1.18.3-rc.1
* Allow building on windows
* Update NDK
* Revert "Updated Syncthing to v1.18.3-rc.1"
This reverts commit 377482c855.
- Use ndk 21 due to Go bug: https://github.com/golang/go/issues/42655
- Use pre-built clang binaries instead of building ourselves
- Build syncthing when creating container to prepopulate modules