[libc++][test] Cleanup typos and unnecessary semicolons (#73435)

I've structured this into a series of commits for even easier reviewing,
if that helps. I could easily split this up into separate P

[libc++][test] Cleanup typos and unnecessary semicolons (#73435)

I've structured this into a series of commits for even easier reviewing,
if that helps. I could easily split this up into separate PRs if
desired, but as this is low-risk with simple edits, I thought one PR
would be easiest.

* Drop unnecessary semicolons after function definitions.
* Cleanup comment typos.
* Cleanup `static_assert` typos.
* Cleanup test code typos.
+ There should be no functional changes, assuming I've changed all
occurrences.
* ~~Fix massive test code typos.~~
+ This was a real problem, but needed more surgery. I reverted those
changes here, and @philnik777 is fixing this properly with #73444.
* clang-formatting as requested by the CI.

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[libc++] <experimental/simd> Add default constructor for class simd/simd_mask (#70424)