Set targetSdkVersion to 10000 for MTS tests targeting current

MTS tests built on unstable branches (e.g. git_master) should be testable on
old system images (e.g. S). However, they run into an error during installation
on older images:
`Requires development platform $<current_codename>, but this is a
release platform`

This CL fixes this issue by updating the target_sdk_version of MTS test apps
targeting current to the magical sdk_version 10000

Bug: 227473065
Test: go build ./java
Test: TH
Change-Id: Ic0358a48a19dc239defbb4ee8ec99225cce75584
diff --git a/java/android_manifest.go b/java/android_manifest.go
index 83cb171..522b664 100644
--- a/java/android_manifest.go
+++ b/java/android_manifest.go
@@ -45,7 +45,11 @@
 // This enables release builds (that run with TARGET_BUILD_APPS=[val...]) to target APIs that have not yet been finalized as part of an SDK
 func targetSdkVersionForManifestFixer(ctx android.ModuleContext, sdkContext android.SdkContext) string {
 	targetSdkVersionSpec := sdkContext.TargetSdkVersion(ctx)
-	if ctx.Config().UnbundledBuildApps() && targetSdkVersionSpec.ApiLevel.IsPreview() {
+	// Return 10000 for modules targeting "current" if either
+	// 1. The module is built in unbundled mode (TARGET_BUILD_APPS not empty)
+	// 2. The module is run as part of MTS, and should be testable on stable branches
+	// TODO(b/240294501): Determine the rules for handling test apexes
+	if targetSdkVersionSpec.ApiLevel.IsPreview() && (ctx.Config().UnbundledBuildApps() || includedInMts(ctx.Module())) {
 		return strconv.Itoa(android.FutureApiLevel.FinalOrFutureInt())
 	}
 	targetSdkVersion, err := targetSdkVersionSpec.EffectiveVersionString(ctx)
@@ -55,6 +59,15 @@
 	return targetSdkVersion
 }
 
+// Helper function that casts android.Module to java.androidTestApp
+// If this type conversion is possible, it queries whether the test app is included in an MTS suite
+func includedInMts(module android.Module) bool {
+	if test, ok := module.(androidTestApp); ok {
+		return test.includedInTestSuite("mts")
+	}
+	return false
+}
+
 type ManifestFixerParams struct {
 	SdkContext             android.SdkContext
 	ClassLoaderContexts    dexpreopt.ClassLoaderContextMap