sycl: add CONCAT operator support (#16047)

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

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Co-authored-by: Sigbjørn Skjæret <redacted>