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[bot]]

Codecov Report

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

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

```diff @@ 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](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/538?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation) | Coverage Δ | | |---|---|---| | [src/Multivariate/ProductFun.jl](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/538?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL011bHRpdmFyaWF0ZS9Qcm9kdWN0RnVuLmps) | `0.00% <0.00%> (ø)` | | | [src/Operators/banded/Conversion.jl](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/538?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL09wZXJhdG9ycy9iYW5kZWQvQ29udmVyc2lvbi5qbA==) | `22.22% <0.00%> (-0.73%)` | :arrow_down: | | [src/eigen.jl](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/538?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL2VpZ2VuLmps) | `0.00% <0.00%> (ø)` | | | [src/Spaces/QuotientSpace.jl](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/538?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL1NwYWNlcy9RdW90aWVudFNwYWNlLmps) | `3.95% <28.57%> (+0.50%)` | :arrow_up: |

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