Preserve axes in permutedims

[jishnub]

The vector method is unnecessary, as the fallback Base method uses reshape, which will do the same.

For the other method:
On master,

julia> F = Fill(2, (SOneTo(2), SOneTo(3)))
2×3 Fill{Int64, 2, Tuple{SOneTo{2}, SOneTo{3}}} with indices SOneTo(2)×SOneTo(3), with entries equal to 2

julia> permutedims(F)
3×2 Fill{Int64, 2, Tuple{SOneTo{3}, SOneTo{2}}} with indices SOneTo(3)×SOneTo(2), with entries equal to 2

julia> permutedims(F, (2,1))
3×2 Fill{Int64}, with entries equal to 2

In the second operation, the static axes are lost. After this PR, the axes are preserved:

julia> permutedims(F, (2,1))
3×2 Fill{Int64, 2, Tuple{SOneTo{3}, SOneTo{2}}} with indices SOneTo(3)×SOneTo(2), with entries equal to 2

To make this type-stable, we require aggressive constant propagation on the permutation tuple.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.83%. Comparing base (5671b89) to head (537c43d).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/fillalgebra.jl	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #319      +/-   ##
==========================================
- Coverage   99.91%   99.83%   -0.09%     
==========================================
  Files           9        9              
  Lines        1200     1200              
==========================================
- Hits         1199     1198       -1     
- Misses          1        2       +1     

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[mtfishman]

@jishnub I just came across a need for this, can this be merged?