Split the Android platform java logic into an Android library module (lib) and an application module (app).

The application module `app` serves double duties of providing the prebuilt Godot binaries ('android_debug.apk', 'android_release.apk') and the Godot custom build template ('android_source.zip').

platform/android/java/THIRDPARTY.md

@@ -1,39 +0,0 @@
-# Third-party libraries
-
-This file list third-party libraries used in the Android source folder,
-with their provenance and, when relevant, modifications made to those files.
-
-## com.android.vending.billing
-
-- Upstream: https://github.com/googlesamples/android-play-billing/tree/master/TrivialDrive/app/src/main
-- Version: git (7a94c69, 2019)
-- License: Apache 2.0
-
-Overwrite the file `aidl/com/android/vending/billing/IInAppBillingService.aidl`.
-
-## com.google.android.vending.expansion.downloader
-
-- Upstream: https://github.com/google/play-apk-expansion/tree/master/apkx_library
-- Version: git (9ecf54e, 2017)
-- License: Apache 2.0
-
-Overwrite all files under:
-
-- `src/com/google/android/vending/expansion/downloader`
-
-Some files have been modified for yet unclear reasons.
-See the `patches/com.google.android.vending.expansion.downloader.patch` file.
-
-## com.google.android.vending.licensing
-
-- Upstream: https://github.com/google/play-licensing/tree/master/lvl_library/
-- Version: git (eb57657, 2018) with modifications
-- License: Apache 2.0
-
-Overwrite all files under:
-
-- `aidl/com/android/vending/licensing`
-- `src/com/google/android/vending/licensing`
-
-Some files have been modified to silence linter errors or fix downstream issues.
-See the `patches/com.google.android.vending.licensing.patch` file.