Mutators are registered into a global variable, and then into the
context when it is created. Only call registerMutators once so that the
same mutator is not listed multiple times in the global variable when
multiple contexts are created.
Test: go test -v android/soong/android
Change-Id: Ie9e3ed09a89b848462b898476cdfb81a90c64bd3
Register mutators inside lambdas that are called in a defined order to
correctly order mutators before and after the arch and deps mutators.
Test: build.ninja identical
Change-Id: Iefe2a3515aee8570e76a6e76925db4cda0e9e822
Mutator registration is tightly coupled with the android package, move
all registration from the soong package to the android package.
Test: build.ninja identical
Change-Id: Ie183d0b52cc7431c9e05b231934d189208ef1efe
