Fix aapt2 --min-sdk-version after finalized SDK

aapt2 --min-sdk-version was using AppsDefaultVersionName(), which
is OMR1 for a non-finalized SDK, but 8.1.0 after finalization.
Add PlatformSdkCodename() for non-finalized SDKs, use it for
DefaultAppTargetSdk(), and pass it for aapt2 --min-sdk-version.

Bug: 78224641
Test: TestAppSdkVersion in app_test.go
Change-Id: I622eaf92f8a940f79007c2a579536da325700b06
diff --git a/android/config.go b/android/config.go
index 7122f48..40ba8c1 100644
--- a/android/config.go
+++ b/android/config.go
@@ -476,6 +476,10 @@
 	return strconv.Itoa(c.PlatformSdkVersionInt())
 }
 
+func (c *config) PlatformSdkCodename() string {
+	return String(c.productVariables.Platform_sdk_codename)
+}
+
 func (c *config) MinSupportedSdkVersion() int {
 	return 14
 }
@@ -488,6 +492,14 @@
 	}
 }
 
+func (c *config) DefaultAppTargetSdk() string {
+	if Bool(c.productVariables.Platform_sdk_final) {
+		return c.PlatformSdkVersion()
+	} else {
+		return c.PlatformSdkCodename()
+	}
+}
+
 func (c *config) AppsDefaultVersionName() string {
 	return String(c.productVariables.AppsDefaultVersionName)
 }