Add test to TestJavaStableSdkVersion for legacy core platform

Adds a test case to TestJavaStableSdkVersion for the case where a
module uses sdk_version: "core_platform" but is in the list of modules
that can use the legacy version.

This required storing the lookup map in the Config to allow it to be
customized for the test.

Bug: 180399951
Test: m nothing
Change-Id: I404705c3fd8a559649c6ab2624856cf78f49f85c