Create sysprop_library soong module

A newly introduced sysprop_library soong module will generate a
java_sdk_library and a cc_library from .sysprop description files.
Both Java modules and C++ modules can link against sysprop_library
module, thus giving consistency for using generated sysprop API.

As Java controls accessibility of Internal / System properties with
@hide and @SystemApi, 2 different header files will be created. And
build system will selectively expose depending on the property owner
and the place where the client libraries go into.

Bug: 80125326
Bug: 122170616
Test: 1) Create sysprop_library module.
Test: 2) Create empty txt files under prebuilts/sdk.
Test: 3) Create api directory, make update-api, and see changes.
Test: 4) Try to link against sysprop_library with various clients.
Test: 5) Soc_specific, Device_specific, Product_specific, recovery flags
work as intended.
Change-Id: I78dc5780ccfbb4b69e5c61dec26b94e92d43c333
diff --git a/android/hooks.go b/android/hooks.go
index 57560d2..6b2468d 100644
--- a/android/hooks.go
+++ b/android/hooks.go
@@ -123,7 +123,7 @@
 	install []func(InstallHookContext)
 }
 
-func loadHookMutator(ctx TopDownMutatorContext) {
+func LoadHookMutator(ctx TopDownMutatorContext) {
 	if m, ok := ctx.Module().(Module); ok {
 		// Cast through *androidTopDownMutatorContext because AppendProperties is implemented
 		// on *androidTopDownMutatorContext but not exposed through TopDownMutatorContext
diff --git a/android/mutator.go b/android/mutator.go
index b77c2f0..e5f742f 100644
--- a/android/mutator.go
+++ b/android/mutator.go
@@ -74,7 +74,7 @@
 
 var preArch = []RegisterMutatorFunc{
 	func(ctx RegisterMutatorsContext) {
-		ctx.TopDown("load_hooks", loadHookMutator).Parallel()
+		ctx.TopDown("load_hooks", LoadHookMutator).Parallel()
 	},
 	RegisterNamespaceMutator,
 	RegisterPrebuiltsPreArchMutators,