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/multitree/Android.bp b/multitree/Android.bp
new file mode 100644
index 0000000..9b16d20
--- /dev/null
+++ b/multitree/Android.bp
@@ -0,0 +1,19 @@
+package {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+bootstrap_go_package {
+    name: "soong-multitree",
+    pkgPath: "android/soong/multitree",
+    deps: [
+        "blueprint",
+        "soong-android",
+    ],
+    srcs: [
+        "api_surface.go",
+        "export.go",
+        "metadata.go",
+        "import.go",
+    ],
+    pluginFor: ["soong_build"],
+}