Add test_mainline_modules to the auto-gen test config(AndroidJUnitTest only).

To support parameterized mainline modules in Test Mapping, we plan to
add a new parameter called test_mainline_modules in build system to
auto-generate the test config based on the parameter.

For detailed information: go/test-mapping-mainline-gcl
(search for auto-generated pattern)

Bug: 155238134
Test: add "test_mainline_modules: [some.apk]" to TetheringTests,
and build the modules, confirm the parameterized option is added
in the test config.

Change-Id: I41ba8749ce46da62db402a8b8a555d4874e1cfc0

java/java.go

@@ -2033,6 +2033,10 @@ type testProperties struct {
 	// doesn't exist next to the Android.bp, this attribute doesn't need to be set to true
 	// explicitly.
 	Auto_gen_config *bool
+
+	// Add parameterized mainline modules to auto generated test config. The options will be
+	// handled by TradeFed to do downloading and installing the specified modules on the device.
+	Test_mainline_modules []string
 }
 
 type testHelperLibraryProperties struct {