Change signed wavefields to B-R colors

[int-ptr-ptr]

Description

Please describe the changes/features in this pull request.

For wavefields

        wavefield_type == specfem::wavefield::type::pressure ||
        wavefield_type == specfem::wavefield::type::rotation ||
        wavefield_type == specfem::wavefield::type::intrinsic_rotation ||
        wavefield_type == specfem::wavefield::type::curl

a blue-red display scheme is used for plot_wavefield.

Issue Number

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Checklist

Please make sure to check developer documentation on specfem docs.

• I ran the code through pre-commit to check style
• THE DOCUMENTATION BUILDS WITHOUT WARNINGS/ERRORS
• I have added labels to the PR (see right hand side of the PR page)
• My code passes all the integration tests
• I have added sufficient unittests to test my changes
• I have added/updated documentation for the changes I am proposing
• I have updated CMakeLists to ensure my code builds
• My code builds across all platforms

[int-ptr-ptr]

One thing that I am not too happy about is how the scaling changes each frame, so a wave that hits a Neumann boundary doubles the table range. Since this solution does not use a sigmoid, it dims the colors everwhere.

That being said, I don't know of any good way to handle that, since the previous sigmoid is way too steep, and acts more like a binary filter, but I think that should be handled in a later PR.