Set JAVA_HOME for runtime via soong AndroidTest.xml template

The jdk used by Robolectric during tests should always be the ANDROID_JAVA_HOME, as such this change, reads that environment variable from the build, and uses it to set the java_folder via the {EXTRA_CONFIGS} in the build/core/robolectric_test_config_template.xml

Test: atest MyRoboTests and look at the generated xml file
Bug: 372520027

Change-Id: Ie63da8602224279f7920c124762cfc29f714c7e1