Move filesystem into Config

The filesystem object was available through ModuleContext.Fs(), but
gives too much access to the filesystem without enforicing correct
dependencies.  In order to support sandboxing the soong_build
process move the filesystem into the Config.  The next change will
make it private.

Bug: 146437378
Test: all Soong tests
Change-Id: I5d3ae9108f120fd335b21efd612aefa078378813

android/variable_test.go

@@ -198,18 +198,11 @@ func TestProductVariables(t *testing.T) {
 			name: "baz",
 		}
 	`
-
-	mockFS := map[string][]byte{
-		"Android.bp": []byte(bp),
-	}
-
-	ctx.MockFileSystem(mockFS)
-
-	ctx.Register()
-
-	config := TestConfig(buildDir, nil)
+	config := TestConfig(buildDir, nil, bp, nil)
 	config.TestProductVariables.Eng = proptools.BoolPtr(true)
 
+	ctx.Register(config)
+
 	_, errs := ctx.ParseFileList(".", []string{"Android.bp"})
 	FailIfErrored(t, errs)
 	_, errs = ctx.PrepareBuildActions(config)