Promote rangespace/domainspace of Conversion

[jishnub]

After this, the following works:

julia> Conversion(Chebyshev(), Ultraspherical(1)) : Ultraspherical(1)
ConversionWrapper : Ultraspherical(1) → Ultraspherical(1)
 1.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅   1.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅   1.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅   1.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅   1.0   ⋅    ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅   1.0   ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   1.0   ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   1.0   ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   1.0   ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   1.0  ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   ⋱

[codecov]

Codecov Report

Patch coverage: 9.52% and project coverage change: -0.02% ⚠️

Comparison is base (27c3236) 27.41% compared to head (6103c79) 27.40%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #538      +/-   ##
==========================================
- Coverage   27.41%   27.40%   -0.02%     
==========================================
  Files          80       80              
  Lines        8363     8370       +7     
==========================================
+ Hits         2293     2294       +1     
- Misses       6070     6076       +6     

Files Changed	Coverage Δ
src/Multivariate/ProductFun.jl	0.00% <0.00%> (ø)
src/Operators/banded/Conversion.jl	22.22% <0.00%> (-0.73%)	⬇️
src/eigen.jl	0.00% <0.00%> (ø)
src/Spaces/QuotientSpace.jl	3.95% <28.57%> (+0.50%)	⬆️

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