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/Android.bp b/cc/Android.bp
index 9103a48..bbc2357 100644
--- a/cc/Android.bp
+++ b/cc/Android.bp
@@ -15,6 +15,7 @@
         "soong-etc",
         "soong-fuzz",
         "soong-genrule",
+        "soong-multitree",
         "soong-snapshot",
         "soong-tradefed",
     ],
@@ -65,6 +66,7 @@
         "library.go",
         "library_headers.go",
         "library_sdk_member.go",
+        "library_stub.go",
         "native_bridge_sdk_trait.go",
         "object.go",
         "test.go",
@@ -94,6 +96,7 @@
         "gen_test.go",
         "genrule_test.go",
         "library_headers_test.go",
+        "library_stub_test.go",
         "library_test.go",
         "object_test.go",
         "prebuilt_test.go",