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/test_data_test.go

@@ -122,10 +122,10 @@ func TestDataTests(t *testing.T) {
 				"dir/baz":        nil,
 				"dir/bar/baz":    nil,
 			})
-			ctx := android.NewTestContext()
+			ctx := android.NewTestContext(config)
 			ctx.RegisterModuleType("filegroup", android.FileGroupFactory)
 			ctx.RegisterModuleType("test", newTest)
-			ctx.Register(config)
+			ctx.Register()
 
 			_, errs := ctx.ParseBlueprintsFiles("Blueprints")
 			android.FailIfErrored(t, errs)