Initializer cleanup

Cleaned up the initialer methods in the parser
and added first-class array initializers.

Passes all WebGL tests.

Change-Id: Ia73db8bfd461f36b717444a8ba4c9ec77d1cee36
Reviewed-on: https://swiftshader-review.googlesource.com/3473
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>