Replace AlignedBoxedSlice with aligned_vec::ABox

[FreezyLemon]

Closes #3370.

ABox<[T]> generally works the same way as AlignedBoxedSlice<T>, but uses a different alignment by default:

AlignedBoxedSlice: 8 on wasm, 64 everywhere else
ABox: Generally two cachelines, 64 bytes for unknown archs (exact rules)

I am pretty sure the wasm allocation bug mentioned in the code comment has been fixed, so using a higher alignment should be fine on the wasm32 arch.

It's possible to configure aligned_vec to reproduce the old behaviour exactly, but I think it's probably better to stick to the crate defaults.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.69%. Comparing base (3c3a26f) to head (66e15b9).
Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3371      +/-   ##
==========================================
+ Coverage   88.52%   88.69%   +0.16%     
==========================================
  Files          89       89              
  Lines       28323    27760     -563     
==========================================
- Hits        25074    24622     -452     
+ Misses       3249     3138     -111     

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[barrbrain]

The aligned_vec crate doesn't appear to be popular enough to have made its way into distributions yet. As it is a transitive dependency via v_frame, this is no worse than the current state.