Improve CUDA compilation

Issue/feature addressed

Various issues caused by enabling Cuda in the redesign, particularly in relation to different flags being applied across host and device phases of compilation, e.g. MSVC flags were mistakenly being used by nvcc during the device compilation phase

Proposed solution

Separate Cmake file added for managing Cuda

Implementation

Activate redesign on win10, default and full built CI.

CMake generator expressions to apply the correct flags for different combinations of compiler and language

pthreads flag in NektarCommon only added when language=C++

Cuda headers given .cuh extension to facilitate easy inclusion

Tweaks to CI to prevent uncompiled files warning

Tests

Suggested reviewers

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Notes

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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).