* Add support for NDK discovery and add --prefer-shared-library option
We would like to be able to use native tools (e.g. simpleperf, gdb) with
precompiled flutter apps. The native tools work much better with *.so
files instead of the custom formats the Dart VM uses by default.
The reason for using blobs / instruction snapshots is that we do not
want to force flutter users to install the Android NDK.
This CL adds a `--prefer-shared-library` flag to e.g. `flutter build
apk` which will use the NDK compiler (if available) to turn the
precompiled app assembly file to an `*.so` file. If the NDK compiler is
not available it will default to the default behavior.
* Rebase, add test for NDK detection, augment flutter.gradle with @Input for flag
* Use InMemoryFileSystem for test
* Remove unused import
* Address some analyzer warnings
Previously, we were mapping certain named platforms
(e.g. `android-stable`) to their corresponding version.
this had two problems:
1. The version could become out of date. For instance, we had
mapped `android-stable` to version 24, but the stable version
is now 27.
2. The list of possible named versions wasn't comprehensive.
Some Android SDKs just list the platform as `stable`, or
`experimental`, etc.
This change updates the platform version detection to use
the `build.prop` file that exists in the platform directory
(only for cases where the version number is not encoded into
the directory name).
