Reland "[MLGO] ML Regalloc Priority Advisor"

This relands commit 8f4f26ba, which was reverted in 91c96a80 because of Buildbot failures. The previous model test is not compatible with tflite. e.g. https://lab.llvm.org/buildbot/#/builders/6/builds/14041

Differential Revision: https://reviews.llvm.org/D133616