Check for elementwise equality when comparing with UniformScaling

[jishnub]

This works around issues with block matrices like:

julia> A = Diagonal(fill(I(2), 4))
4×4 Diagonal{Diagonal{Bool, Vector{Bool}}, Vector{Diagonal{Bool, Vector{Bool}}}}:
 Diagonal(Bool[1, 1])  …        ⋅       
       ⋅                        ⋅       
       ⋅                        ⋅       
       ⋅                  Diagonal(Bool[1, 1])

julia> A == I
true

julia> A[1,1] == I[1,1]
false

The checks in this PR ensure that if a matrix is == a UniformScaling, their elements are equal as well.

This builds on top of #1367, and may be rebased once that is merged.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.81%. Comparing base (5f449f5) to head (b38651a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1369      +/-   ##
==========================================
- Coverage   93.81%   93.81%   -0.01%     
==========================================
  Files          34       34              
  Lines       15717    15716       -1     
==========================================
- Hits        14745    14744       -1     
  Misses        972      972              

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