monorepo.

Make LICENSE.txt and the corresponding patch file match https://github.com/stepancheg/rust-protobuf/blob/master/protobuf-parse/LICENSE.txt

Make LICENSE a symlink to LICENSE.txt.

Bug: http://b/339424309
Test: treehugger
Change-Id: I7729fa29ab6fa4f7f7ed9e0d442edbb2cfb17570