Prototype changes for multitree

This change contains a prototype implementation for multitree. Several
interfaces and modules are added.

1. Imported/Exported
Modules implementing Exportable interface can export artifacts to other
components. "imported_filegroup" modules can import generated artifacts from other exported modules.

2. Multitree metadata
It contains information about imported/exported modules in each
component, and can be generated via "m update-meta".

3. cc library stub
It's based on prototype stub libraries. It uses imported/exported
mechanism to expose a C API, with a map.txt file and header files.

Bug: 230448564
Test: m
Change-Id: Id7ff7618e2c630c5617a564d8b23b60a1cc9c8e8
diff --git a/cc/ndk_library.go b/cc/ndk_library.go
index 5ef41ea..c031b14 100644
--- a/cc/ndk_library.go
+++ b/cc/ndk_library.go
@@ -93,7 +93,7 @@
 type libraryProperties struct {
 	// Relative path to the symbol map.
 	// An example file can be seen here: TODO(danalbert): Make an example.
-	Symbol_file *string
+	Symbol_file *string `android:"path"`
 
 	// The first API level a library was available. A library will be generated
 	// for every API level beginning with this one.