Draft: Initial version of advection operator for stdmat approach

Issue/feature addressed

Add a DG advection operator for the StdMat approach.

Proposed solution

See above.

Implementation

Added a new operator named OpAdvection (prefix Op to avoid confusion with legacy Advection operators). At this point the StdMat approach is being implemented.

Tests

• Standard Unit tests for the redesign framework testing all element types.

Suggested reviewers

Jacques Xing, Chris Cantwell, Boyang Xia

Notes

• We do not have a way of handling Point geometry types yet. That's why the DG framework does not use the Segment test cases.

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).