Split Fixtures up and cleaned test headers

[jessemapel]

Description

Split the giant Fixtures.h file into multiple files so that we're only including what we need in each test. There were many tests that were depending on Fixtures.h to include headers for them, so I also went through and added a bunch of includes to individual files.

Related Issue

Fixing CI

Motivation and Context

This should dramatically reduce the amount of stuff the compiler has to deal with when compiling the tests. So, they will compile faster and hopefully take less resources getting our CI building correctly again.

This will also reduce the number of test files that need to be recompiled when modifying or adding a fixture.

How Has This Been Tested?

Tests still build correctly on my system.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation change (update to the documentation; no code change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read and agree to abide by the Code of Conduct
• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have added myself to the .zenodo.json document.
• I have added any user impacting changes to the CHANGELOG.md document.

Licensing

This project is mostly composed of free and unencumbered software released into the public domain, and we are unlikely to accept contributions that are not also released into the public domain. Somewhere near the top of each file should have these words:

This work is free and unencumbered software released into the public domain. In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain.

• I dedicate any and all copyright interest in this software to the public domain. I make this dedication for the benefit of the public at large and to the detriment of my heirs and successors. I intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.

[jessemapel]

I left file here for two reasons:

1. If anyone adds new fixtures in an existing PR, this file will still be here and they won't need to deal with merge conflicts
2. You can still just include all of the fixtures by including this file because it includes the split up files now.