Support new "prefab" AAR format

[atsushieno]

Starting with Android Gradle Plugin 4.0 Canary 9, Google has introduced a completely new AAR archive format called "prefab" which is to bundle native libraries as well as header files, so that (for AGP) adding simple reference to the Maven artifact ID will automatically resolve those header files when AGP builds a referencing project that depends on such an AAR.

https://developer.android.com/studio/preview/features?buildsystem=cmake#native-dependencies

It already takes place in some libraries. For example, see https://github.com/google/oboe/blob/master/docs/GettingStarted.md#option-1-using-pre-built-binaries-and-headers

Below you will find how such an AAR looks different from former ones:

$ unzip -l ~/Downloads/oboe-1.3.0.aar
Archive:  /home/atsushi/Downloads/oboe-1.3.0.aar
  Length      Date    Time    Name
---------  ---------- -----   ----
      227  2020-02-14 19:39   AndroidManifest.xml
...
     3912  2019-10-18 21:27   prefab/modules/oboe/include/oboe/LatencyTuner.h
     3072  2020-02-20 02:48   prefab/modules/oboe/include/oboe/Version.h
...
     1106  2019-10-18 21:27   prefab/modules/oboe/include/oboe/Oboe.h
    16390  2020-02-20 02:48   prefab/modules/oboe/include/oboe/Definitions.h
...
  1935088  2020-02-20 03:06   prefab/modules/oboe/libs/android.x86_64/liboboe.so
       53  2020-02-14 07:48   prefab/modules/oboe/libs/android.x86_64/abi.json
        0  2020-02-20 03:05   prefab/modules/oboe/libs/android.arm64-v8a/
     6148  2020-02-20 02:57   prefab/modules/oboe/libs/android.arm64-v8a/.DS_Store
  1981584  2020-02-20 03:05   prefab/modules/oboe/libs/android.arm64-v8a/liboboe.so
       56  2020-02-14 07:48   prefab/modules/oboe/libs/android.arm64-v8a/abi.json
...
      137  2020-02-14 00:10   prefab/modules/oboe/module.json
       95  2020-02-14 00:55   prefab/prefab.json
---------                     -------
  8607500                     38 files

You will most likely have to support those new AAR packages to build bindings.

[atsushieno]

FYI microsoft/vcpkg#10271