Support tagged module references

There are cases where a module needs to refer to an intermediate
output of another module instead of its final output.  For example,
a module may want to use the .jar containing .class files from
another module whose final output is a .jar containing classes.dex
files.  Support a new ":module{.tag}" format in any property that
is annotated with `android:"path"`, which will query the target
module for its ".tag" output(s).

Test: path_properties_test.go, paths_test.go
Test: no unexpected changes in build.ninja
Change-Id: Icd3c9b0d83ff125771767c04046fcffb9fc3f65a

android/path_properties_test.go

@@ -41,8 +41,10 @@ func pathDepsMutatorTestModuleFactory() Module {
 }
 
 func (p *pathDepsMutatorTestModule) GenerateAndroidBuildActions(ctx ModuleContext) {
-	ctx.VisitDirectDepsWithTag(SourceDepTag, func(dep Module) {
-		p.sourceDeps = append(p.sourceDeps, ctx.OtherModuleName(dep))
+	ctx.VisitDirectDeps(func(dep Module) {
+		if _, ok := ctx.OtherModuleDependencyTag(dep).(sourceOrOutputDependencyTag); ok {
+			p.sourceDeps = append(p.sourceDeps, ctx.OtherModuleName(dep))
+		}
 	})
 }
 
@@ -59,7 +61,7 @@ func TestPathDepsMutator(t *testing.T) {
 				name: "foo",
 				foo: ":a",
 				bar: [":b"],
-				baz: ":c",
+				baz: ":c{.bar}",
 				qux: ":d",
 			}`,
 			deps: []string{"a", "b", "c"},