Extract SDK config that varies downstream to Gradle properties

Also does a minor bit of refactoring to move global config items to
extension properties on the project. This will help us keep things
more organized in the future.

All of the usages in build.gradle should be removed in a future CL
by the PP APIs team.

Bug: 287273074
Test: SdkResourceGeneratorTest
Change-Id: I84bbbded7fcd1216daea71d29834ea8cb0f3ac0c
diff --git a/playground-common/androidx-shared.properties b/playground-common/androidx-shared.properties
index 01e4d08..8fd3212 100644
--- a/playground-common/androidx-shared.properties
+++ b/playground-common/androidx-shared.properties
@@ -45,6 +45,9 @@
 # Generate versioned API files
 androidx.writeVersionedApiFiles=true
 
+androidx.compileSdkVersion=android-34
+androidx.targetSdkVersion=34
+
 # Disable features we do not use
 android.defaults.buildfeatures.aidl=false
 android.defaults.buildfeatures.buildconfig=false
@@ -78,5 +81,3 @@
 # androidx.compose.multiplatformEnabled=true
 
 kotlin.mpp.androidSourceSetLayoutVersion=1
-
-