Add overrides support for snapshots

Overrides properties will now be captured in json flag files, which will
be copied to installed vendor snapshot modules.

Bug: 216567575
Test: soong test && manual install
Change-Id: Ife5e84b126e798fba7802b9cff000c9197756cb9

cc/cc.go

@@ -616,6 +616,10 @@ type xref interface {
 	XrefCcFiles() android.Paths
 }
 
+type overridable interface {
+	overriddenModules() []string
+}
+
 type libraryDependencyKind int
 
 const (
@@ -3637,6 +3641,13 @@ func (c *Module) UniqueApexVariations() bool {
 	return c.UseVndk() && c.IsVndk()
 }
 
+func (c *Module) overriddenModules() []string {
+	if o, ok := c.linker.(overridable); ok {
+		return o.overriddenModules()
+	}
+	return nil
+}
+
 var _ snapshot.RelativeInstallPath = (*Module)(nil)
 
 type moduleType int