Upwind SBP on curved meshes

[andrewwinters5000]

This PR replaces #1295 . Implementation of the upwind FDSBP solver on unstructured curvilinear meshes. The solver converges for all available splittings and is free-stream preserving provided the boundary polynomial order from the mesh file, i.e., mesh_polydeg is half the boundary closure order of the SBP operator.

[github-actions[bot]]

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.97297% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 96.29%. Comparing base (e205b06) to head (40f6547).

Files	Patch %	Lines
src/solvers/fdsbp_unstructured/fdsbp_2d.jl	92.11%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1857 +/- ## ========================================== + Coverage 96.28% 96.29% +0.01% ========================================== Files 438 438 Lines 35386 35519 +133 ========================================== + Hits 34071 34201 +130 - Misses 1315 1318 +3 ``` | [Flag](https://app.codecov.io/gh/trixi-framework/Trixi.jl/pull/1857/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trixi-framework) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/trixi-framework/Trixi.jl/pull/1857/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trixi-framework) | `96.29% <97.97%> (+0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trixi-framework#carryforward-flags-in-the-pull-request-comment) to find out more.

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[andrewwinters5000]

Thanks a lot! I will merge this and release a new Trixi.jl version when CI passes (whereever it can...)

Great, thanks! It is nice to have finally figured out all this curvilinear upwind stuff. I will close my old PR and delete that (very stale) branch.