Merge pull request dotnet/coreclr#6533 from pgavlin/LSRA

Replace the LSRA stack with a hash table.

Commit migrated from https://github.com/dotnet/coreclr/commit/d7ca197675ef4e17ad3d7eaa4f14f364557fa2a3

diff --cc src/coreclr/src/jit/gentree.cpp
Simple merge

diff --cc src/coreclr/src/jit/gentree.h
Simple merge

diff --cc src/coreclr/src/jit/lower.cpp
Simple merge

diff --cc src/coreclr/src/jit/lsra.cpp
Simple merge

diff --cc src/coreclr/src/jit/lsra.h
Simple merge