SYCL Headers use vector aliases which doesn't exist in SYCL spec

[AlexeySachkov]

Describe the bug

SYCL 2020 spec describes different set of vector aliases comparing to SYCL 1.2.1 spec

In particular, aliases like cl_int2 -> vec<cl_int, 2> are now don't exist in the spec. However, they are still used in our implementation, for example:

llvm/sycl/include/sycl/accessor.hpp

Lines 776 to 780 in ffda344

	template <int Dims = Dimensions, typename = detail::enable_if_t<Dims == 2>>
	range<2> get_range() const {
	cl_int2 Range = getRangeInternal();
	return range<2>(Range[0], Range[1]);
	}

I suppose that we want to get rid of those extra aliases to simplify our codebase and maintenance effort, but before doing so, we need to stop using those aliases internally first.

[AlexeySachkov]

There is a PR #7915 which intended to fix this

[AlexeySachkov]

I submitted a bunch of PRs which cleaned up our implementation and legacy aliases were deprecated in #8561 and #8541. We have a test which checks that we don't use them in our headers anymore. Therefore, closing this