Compile Git for host and Android target platforms

- Rename CrossCompileGitForAndroid.sh to CompileGitForAllTargetPlatforms.sh and support host, Android-only, and all-target modes.
- Compile a development-host Git binary at build/host-git/libgit.so for JVM tests.
- Route level and sandbox tests through GITHUG_TEST_GIT_BINARY so they exercise the compiled host Git rather than the system Git fallback.
- Cross-compile packaged Git binaries for arm64-v8a, armeabi-v7a, x86, and x86_64 Android targets.
- Remove the temporary device-bound Pull rebase instrumentation path from the previous debugging attempt.

app/build.gradle.kts

@@ -19,8 +19,8 @@ android {
         applicationId = "solutions.tretter.githugandroid"
         minSdk = 26
         targetSdk = 35
-        versionCode = 122
-        versionName = "0.1.121"
+        versionCode = 123
+        versionName = "0.1.122"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
         vectorDrawables.useSupportLibrary = true