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/android/config.go b/android/config.go
index 9f1fd6a..df3695c 100644
--- a/android/config.go
+++ b/android/config.go
@@ -1482,6 +1482,10 @@
 	return c.productVariables.MissingUsesLibraries
 }
 
+func (c *config) TargetMultitreeUpdateMeta() bool {
+	return c.productVariables.MultitreeUpdateMeta
+}
+
 func (c *deviceConfig) DeviceArch() string {
 	return String(c.config.productVariables.DeviceArch)
 }