This commit moves the shuffle and shuffle2 builtins to the CLC library.
In so doing it makes the headers simpler and re-usable for other builtin
layers to hook into the CLC functions, if they wish.
An additional gentype utility has been made available, which provides a
consistent vector-size-or-1 macro for use.
The existing __CLC_VECSIZE is defined but empty which is useful in
certain applications, such as in concatenation with a type to make a
correctly sized scalar or vector type. However, this isn't usable in the
same preprocessor lines when wanting to check for specific vector sizes,
as e.g., '__CLC_VECSIZE == 2' resolves to '== 2' which is invalid. In
local testing this is also useful for the geometric builtins which are
only available for scalar types and vector types of 2, 3, or 4 elements.
No codegen changes are observed, except the internal shuffle/shuffle2
utility functions are no longer made publicly available.
