Store SingletonMakeVarsProviders in the config

Store SingletonMakeVarsProviders in the config instead of a global
variable to avoid races between tests running in parallel.

Test: all soong tests
Change-Id: I2ab64f368b5ac673fd985399d4421ed018abc562
diff --git a/java/java_test.go b/java/java_test.go
index 87d6ebb..5cc97b3 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -92,8 +92,8 @@
 
 	ctx.PreDepsMutators(python.RegisterPythonPreDepsMutators)
 	ctx.PostDepsMutators(android.RegisterOverridePostDepsMutators)
-	ctx.RegisterPreSingletonType("overlay", android.SingletonFactoryAdaptor(OverlaySingletonFactory))
-	ctx.RegisterPreSingletonType("sdk_versions", android.SingletonFactoryAdaptor(sdkPreSingletonFactory))
+	ctx.RegisterPreSingletonType("overlay", android.SingletonFactoryAdaptor(ctx.Context, OverlaySingletonFactory))
+	ctx.RegisterPreSingletonType("sdk_versions", android.SingletonFactoryAdaptor(ctx.Context, sdkPreSingletonFactory))
 
 	android.RegisterPrebuiltMutators(ctx)