Fix Issue 10386: Make std.math.isIdentical work in CTFE with coverage tests

[runiixx]

I took the modifications @n8sh made in math.d and moved in traits.d since math.d doesn't exist anymore and the math library is now composed of multiple files, and then added more tests because the piece of code that is interpreted in CTFE wasn't covered.
Credit to @n8sh for the code in isIdentical.

[dlang-bot]

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[LightBender]

We are no longer using or linking to Bugzilla for Phobos. I have updated the PR title, but can you please update the commit message to reference the corresponding GH Issue here: #10386