Added TParseContext::addFunctionCallOrMethod() to move function
creation functionality out of glslang.y.

Change-Id: Ia23e8c2490ba9d2bb1fcd00a1ef06eab5cf60b80
Reviewed-on: https://swiftshader-review.googlesource.com/3640Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>