vlc-debian-android: install the NDK in the location gradle would install it

It's using the full version name to install and use NDK, based on the ndkVersion it uses.

• And set a version for the platform-tools so we have reliable versions between Docker runs.
• And use build tools 35 (the default in Android Gradle Plugin 8.9.1 which is downloaded as we don't specify our version to use)
• add a gradle in the PATH (so we don't need to download it every time)

Draft on top of !328 (merged) (3 new commit)