Enhance distribution reuse: `android_api`

[opacam]

In here we solve a problem we have when changing android_api if we already have a build distribution that we can reuse. The problem is that the changes are not reflected in the final APK, because there is some hardcoded android_api in some of the distribution files. So in here we will update those files so when we perform the build of the APK with gradle it will change the necessary stuff with the new android_api.

We also:

• Store the android_api value to dist_info.json file (and update it if we reuse the dist with a new android_api)
• Prettify dist_info.json (to be easier to read it for us)
• Reduce complexity of Distribution.get_distributions
• Add unittests for the added code

How to test this

Well, it will require two builds, the first one with one android_api and then another with a new android_api. Once the second build complete you will see that the distribution file: AndroidManifest.xml has the value of the second build (btw, we never modify this file in this PR, this file is modified by gradle). You can check around line 22, for something like:

    <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="28" />

The value of android:targetSdkVersion should be the one you used with android_api in your second build.

How will look like the dist_info.json file

{
    "android_api": 28,
    "archs": [
        "arm64-v8a"
    ],
    "bootstrap": "sdl2",
    "dist_name": "bdisttest_python3_sqlite_openssl_googlendk",
    "hostpython": "/home/opacam/.local/share/python-for-android/build/other_builds/hostpython3/desktop/hostpython3/native-build/python3",
    "ndk_api": 21,
    "python_version": "3.7",
    "recipes": [
        "hostpython3",
        "libffi",
        "openssl",
        "sdl2_image",
        "sdl2_mixer",
        "sdl2_ttf",
        "sqlite3",
        "python3",
        "sdl2",
        "setuptools",
        "requests",
        "six",
        "pyjnius",
        "android",
        "kivy",
        "peewee"
    ],
    "use_setup_py": false
}

As you see, the keys are sorted and indented with 4 spaces :wink:...imho, far readable than all in one line, right?

Notes

Some parts of the code where taken from #1926, so this PR is a portion of what we presented there, but refreshed and enhanced.

[inclement]

Thanks @opacam, that's a great improvement. Just to let you know I've seen this, but probably won't be able to review it for a few days.

[opacam]

Thanks @opacam, that's a great improvement. Just to let you know I've seen this, but probably won't be able to review it for a few days.

@inclement, no problem at all, this way we can polish this thing thanks to the @AndreMiras review :wink:

@AndreMiras, I will take care of your comments ASAP...I did a quick look to your comments and I see that we can do a little refactoring, nice !! :satisfied:

[Fak3]

Just a thought - could this dist-info.json also be used to hold the environment variables for debugging purposes? Currently they only exist in the temp file during build, so some time ago I raised a PR to keep this file permanently inside the dist dir: https://github.com/kivy/python-for-android/pull/1902