Spirv-opt has not had to handle module with function declarations. This
lead many passes to assume that every function has a body. This is not
always true. This commit will modify a number of passes to handle
function declarations.
Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/4443
* Combines OpAccessChain, OpInBoundsAccessChain, OpPtrAccessChain and
OpInBoundsPtrAccessChain
* New folding rule to fold add with 0 for integers
* Converts to a bitcast if the result type does not match the operand
type
V
