After we refactor the magic mount and always mount folder as tmpfs,
we can easily support deleting files or folders now. We recognize
dummy devices with major number 0 and minor number 0 as an indicator
for removing files and folders. This indicator is borrowed from
overlayfs.
Since Android 15, all domains are allowed to search /metadata so preinit
dir will be exposed. Use /metadata/watchdog when /metadata is chosen as
preinit device, and the dir is available (since Android 11).
The test APK and the main APK share the same process and classloader,
and in the non-hidden case, the test APK's classes take precedence over
the ones in the main APK. This causes issues because the test APK and
main APK share some dependencies, but don't always use the same
version. This is especially problematic for the Kotlin stdlib and
AndroidX dependencies.
The solution here is to rely on R8's obfuscation feature and repackage
all potentially conflicting classes into a separate package in the test
APK. To ensure that the test classes are always using the same classes
as the main APK, we have to directly implement all tests inside the main
APK, making the test APK purely a "test runner with test dependencies".
As a result, the test APK can only be used when built in release mode,
because R8 no longer allow class obfuscation to be enabled when building
for debug versions.
