Use tree representation for class loader context in Make.

Previously Make class loader contexts used a simplified one-level map.
Now they use the same tree representation as in Soong. The difference
between Make and Soong represenataions is insubstantial and caused only
by the language differences between JSON and Go.

Bug: 132357300
Test: lunch aosp_cf_x86_phone-userdebug && m
Change-Id: Ia273afb7f026dbe3b25d4327d55143657b026b98