New dimension mapping

[Tokazama]

Why do this and what are the objectives

The primary focus here is to replace the to_parent_dims and from_parent_dims methods which were only really being used for SubArray, Adjoint, Transpose, and PermutedDimsArray. The point of those methods was originally to avoid repeatedly doing verbose extraction of the permutations for those last three arrays and to consolidate the number of generated functions for mapping across the indices of SubArray. However, there are some problems with SubArray that require more than simple dimension to dimension mapping.

The main goal here is to have something that actually produces an accurate dimension mapping for SubArray. A sort of secondary goal is to reduce many of the generated functions we've needed to support SubArray. Inference is working on local tests (Julia v1.6, v1.7, v1.8,) but seems to be failing CI on v1.6 for some reason. I guess I'll have to do some trial and error there through multiple PRs.

This is not a proposal for a formal interface at this time.
In fact, I'm just removing the formal dimension mapping that to_parent_dims and from_parent_dims composed, because it just wasn't working.
I've tried to include a lengthy explanation of how the internals work in the code comments so everyone knows what's going on as we move forward.

Points of Review

@chriselrod, it appears this is still safe for the LV stuff (which was my main concern moving forward with a release). I would think it's possible to replace the generated function for dense_dims that SubArray requires but I haven't had time to figure out what's going on with that code there yet. I welcome any ideas you have to simplify that but I probably won't have time to figure it out and replace it with something that isn't generated and is performant.
Other than that, I've checked that the methods I'm removing aren't used in any currently used version of ArrayInterface in downstream packaging.

[codecov]

Codecov Report

Merging #327 (93dde6c) into master (1c6c725) will decrease coverage by 0.94%.
The diff coverage is 90.90%.

@@            Coverage Diff             @@
##           master     #327      +/-   ##
==========================================
- Coverage   91.10%   90.16%   -0.95%     
==========================================
  Files           9        9              
  Lines        1462     1342     -120     
==========================================
- Hits         1332     1210     -122     
- Misses        130      132       +2     

Impacted Files	Coverage Δ
src/ArrayInterface.jl	86.06% <ø> (-0.12%)	⬇️
src/size.jl	91.89% <85.71%> (+1.37%)	⬆️
src/indexing.jl	84.37% <87.50%> (-3.58%)	⬇️
src/dimensions.jl	93.57% <90.16%> (-2.34%)	⬇️
src/stridelayout.jl	89.60% <90.36%> (-0.94%)	⬇️
src/axes.jl	92.53% <100.00%> (-0.23%)	⬇️

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[chriselrod]

I don't think removing @generated is a high priority/it can be done in a later PR.