Handle license conversions in androidmk

1. Support license conversions in the androidmk tool. More details can be
found at go/license-androidmk;
2. As usage examples, locally this functionality has been applied to
aosp/1881088 and aosp/1869664;

Bug: 202964622
Test: m androidmk
Test: manually ran androidmk <typical Android.mk files>
Test: TreeHugger
Change-Id: I7d5013d25ad8961e997109d0378f20f5085e0ecf