Merge pull request dotnet/coreclr#6098 from CarolEidt/BlkNodeRefactors

More Blk Op Refactoring

Commit migrated from https://github.com/dotnet/coreclr/commit/9990ac928903d556c635a8d4162a4907c4e41eb1

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

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/importer.cpp
Simple merge

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