Enable R8 full mode by default for apps

This provides significant size savings over the default compatibility
mode, roughly ~20MB in aggregate for a recent Pixel build. Targets can opt out using `proguard_compatibility = true`.

Future work will enable for all targets, not just apps, but this
incremental change yields the most benefit.

Bug: 215530220
Test: m + presubmit
Change-Id: I52a9b27ebe71835849e200e23ae2a250eaf1bbe1

java/app.go

@@ -1030,6 +1030,7 @@ func AndroidAppFactory() android.Module {
 
 	module.Module.dexProperties.Optimize.EnabledByDefault = true
 	module.Module.dexProperties.Optimize.Shrink = proptools.BoolPtr(true)
+	module.Module.dexProperties.Optimize.Proguard_compatibility = proptools.BoolPtr(false)
 
 	module.Module.properties.Instrument = true
 	module.Module.properties.Supports_static_instrumentation = true

java/dex.go

@@ -45,8 +45,8 @@ type DexProperties struct {
 		// Whether to continue building even if warnings are emitted.  Defaults to true.
 		Ignore_warnings *bool
 
-		// If true, runs R8 in Proguard compatibility mode (default).
-		// Otherwise, runs R8 in full mode.
+		// If true, runs R8 in Proguard compatibility mode, otherwise runs R8 in full mode.
+		// Defaults to false for apps, true for libraries and tests.
 		Proguard_compatibility *bool
 
 		// If true, optimize for size by removing unused code.  Defaults to true for apps,