Add pass to reaplce invalid opcodes

Add pass to reaplce invalid opcodes

Creates a pass that will remove instructions that are invalid for the
current shader stage.  For the instruction to be considered for replacement

1) The opcode must be valid for a shader modules.
2) The opcode must be invalid for the current shader stage.
3) All entry points to the module must be for the same shader stage.
4) The function containing the instruction must be reachable from an entry point.

Fixes #1247.