Binary math cleanup

Moved functionality related to binary math
into TParseContext.

No WebGL tests were hurt in the making of this CL.

Change-Id: I51b9aa8f98ceedc4e4a93b4b907d264086157c18
Reviewed-on: https://swiftshader-review.googlesource.com/3512
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>