Ensure that *bootclasspath* module types depend on device variants

Needed to allow change https://r.android.com/2089503 to be reapplied.

Bug: 232106778
Test: Apply the change and then run
      m EMMA_INSTRUMENT=true nothing
Change-Id: I92d19c51cc828295ba13951e65911db707f0f2ba

java/platform_bootclasspath_test.go

@@ -51,6 +51,7 @@ func TestPlatformBootclasspath(t *testing.T) {
 	var addSourceBootclassPathModule = android.FixtureAddTextFile("source/Android.bp", `
 		java_library {
 			name: "foo",
+			host_supported: true, // verify that b/232106778 is fixed
 			srcs: ["a.java"],
 			system_modules: "none",
 			sdk_version: "none",