[OpenCL] Guard write_only image3d_t with TypeExtension

Ensure that the TypeExtension of an `ImageType` is also taken into
account when generating `OpenCLBuiltins.inc`.

This aligns the handling of the `write_only image3d_t` type for
`-fdeclare-opencl-builtins` with opencl-c.h with respect to the
`cl_khr_3d_image_writes` extension.

Since the `write_only image3d_t` type is not available when the
extension is disabled, this commit does not add a test to
`SemaOpenCL/fdeclare-opencl-builtins.cl`.