[SYCL][NFC] Reduce amount of includes in in-tree tests

[AlexeySachkov]

This PR is an attempt to speed up our in-tree tests, main changes are the following:

• add -fsyntax-only to tests which don't launch compiled binaries
• replace single sycl/sycl.hpp include with several includes for only necessary things
• refactored some tests so they don't require queue at all

Had to do some adjustments to a couple of SYCL header files to make them useable in isolation.

Currently, single check-sycl pass takes ~110+ seconds in GitHub Actions. Let's see how that can be improved

[bader]

@AlexeySachkov, ping.

[AlexeySachkov]

@AlexeySachkov, ping.

@bader, I though about this PR and I don't think that it worth much to reduce amount of includes in those headers: I don't see any compile-time improvement, but the maintenance cost increases. Therefore, I will close this PR.

However, there are couple of improvements which could be done anyway:

• using -fsyntax-only in more tests, see [SYCL][NFC] Use -fsyntax-only more extensively in LIT tests #8144
• rewriting more LIT tests into unit-tests, see [SYCL][NFC] Refactor some LIT tests to unit-test #8129 as an example, but more PRs will follow