Complete size templating of LinAdvDiffReaction and for SYCL backend

Issue/feature addressed

The SYCL backend were not properly templated for the size parameters. This MR solves this issue.

Proposed solution

Implementation

Tests

Suggested reviewers

Notes

Due to excessive compilation time, size-based templating is disable for the SYCL backend in debug mode for the Gitlab CI.

Checklist

• Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• [ ] Changelog is updated.
• [ ] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).