Auto generate recovery build.prop module

Implementation details:
- Introduce recovery_build_prop module type given that the build rule of
  the recovery partition's build.prop file is quite different from that
  of the other partitions' build.prop files.
- Modify the visibility of the Soong-defined build_prop modules to allow
  the recovery_build_prop module to depend on them.
- Auto generate the recovery_build_prop module and add it to deps in
  FsGenState.

Test: build soong generated recovery partition and inspect the content of the generated prop.default file
Bug: 381888358
Change-Id: I17eaa969da245863c11fab259fbbbb81aa46dfc4
diff --git a/android/variable.go b/android/variable.go
index 19f63e3..69e0337 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -688,6 +688,8 @@
 	ProductFsverityGenerateMetadata bool `json:",omitempty"`
 
 	TargetScreenDensity string `json:",omitempty"`
+
+	PrivateRecoveryUiProperties map[string]string `json:",omitempty"`
 }
 
 func boolPtr(v bool) *bool {