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
diff --git a/java/dexpreopt_bootjars_test.go b/java/dexpreopt_bootjars_test.go
index ab31958..95fe5e1 100644
--- a/java/dexpreopt_bootjars_test.go
+++ b/java/dexpreopt_bootjars_test.go
@@ -51,7 +51,7 @@
 	dexpreoptConfig.BootJars = android.CreateTestConfiguredJarList([]string{"platform:foo", "platform:bar", "platform:baz"})
 	dexpreopt.SetTestGlobalConfig(config, dexpreoptConfig)
 
-	ctx := testContext()
+	ctx := testContext(config)
 	RegisterDexpreoptBootJarsComponents(ctx)
 	run(t, ctx, config)