export_proguard_spec for libs deps

Add a property to export proguard flags files for libs dependencies.
Currently only proguard flags files from static deps are propagated up
to reverse dependencies, but it is necessary sometimes to have flags
from libs dependencies also be propagated.

Bug: 289087274
Test: go test ./java
Change-Id: Ic0aa22b086792bf322041aa5780db6c4f4eb2770

java/dex.go

@@ -71,6 +71,10 @@ type DexProperties struct {
 
 		// Specifies the locations of files containing proguard flags.
 		Proguard_flags_files []string `android:"path"`
+
+		// If true, transitive reverse dependencies of this module will have this
+		// module's proguard spec appended to their optimization action
+		Export_proguard_flags_files *bool
 	}
 
 	// Keep the data uncompressed. We always need uncompressed dex for execution,