Add support for cc_library_headers to replace llndk_headers

Set llndk.llndk_headers: true to allow a cc_library_headers
module to be used by a cc_library module with llndk.symbol_file set.

Bug: 170784825
Test: TestLlndkHeaders
Change-Id: Ib65a4b70717dc9a54ae30f2991485bb1bb9b8409

cc/llndk_library.go

@@ -69,6 +69,10 @@ type llndkLibraryProperties struct {
 	// vendor nor product libraries. This effectively hides this module from
 	// non-system modules. Default value is false.
 	Private *bool
+
+	// if true, make this module available to provide headers to other modules that set
+	// llndk.symbol_file.
+	Llndk_headers *bool
 }
 
 type llndkStubDecorator struct {