Merge pull request dotnet/coreclr#12540 from pgavlin/OperandVisitor

Add a generic operand visitor to `GenTree`.

Commit migrated from https://github.com/dotnet/coreclr/commit/f9153d20ab61808722a8a2d91c75e08e32a0c765

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