sycl: add CONCAT operator support (#16047)
* sycl: add CONCAT operator support
* cleanup: remove stray lines added by mistake
* fix: code format issues in concat.cpp and tests/test-backend-ops.cpp
* chore: fix editorconfig violations
* cleanup: drop unnecessary i16 type support
* docs: update sycl-csv and regenerate ops.md
* update docs/ops.md
* fix: adapt to upstream master changes after rebase
* fix: remove empty files
* fix: drop whitespace
---------
Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>
