Pass Config to NewTestContext instead of ctx.Register

Prepare for using Config when adding singletons by passing
Config to NewTestContext and NewContext instead of to ctx.Register.
This will enable a followup change to store SingletonMakeVarsProviders
registered on the Context in the Config, which is necessary to run
multiple tests in parallel without data races.

Test: all soong tests
Change-Id: Id229629a4e42ff4487d317241673837726c075fc

cc/prebuilt_test.go

@@ -25,7 +25,7 @@ import (
 
 func testPrebuilt(t *testing.T, bp string, fs map[string][]byte, handlers ...configCustomizer) *android.TestContext {
 	config := TestConfig(buildDir, android.Android, nil, bp, fs)
-	ctx := CreateTestContext()
+	ctx := CreateTestContext(config)
 
 	// Enable androidmk support.
 	// * Register the singleton
@@ -38,7 +38,7 @@ func testPrebuilt(t *testing.T, bp string, fs map[string][]byte, handlers ...con
 		handler(config)
 	}
 
-	ctx.Register(config)
+	ctx.Register()
 	_, errs := ctx.ParseFileList(".", []string{"Android.bp"})
 	android.FailIfErrored(t, errs)
 	_, errs = ctx.PrepareBuildActions(config)