Merge pull request #7294 from pgavlin/longLclFld

Implement `st.lclFld` decomposition and fix #6778.

diff --cc src/jit/codegenxarch.cpp
Simple merge

diff --cc src/jit/decomposelongs.cpp
Simple merge

diff --cc src/jit/decomposelongs.h
Simple merge

diff --cc src/jit/lclvars.cpp
Simple merge

diff --cc src/jit/liveness.cpp
Simple merge

diff --cc src/jit/lowerxarch.cpp
Simple merge

diff --cc tests/issues.targets
Simple merge