TensorSpace in ProductFun constructor

[jishnub]

After this,

julia> P = ProductFun((x,y) -> x*y, Chebyshev()^2)
ProductFun on Chebyshev() ⊗ Chebyshev()

julia> Q = (Derivative() ⊗ I) * P
ProductFun on Ultraspherical(1) ⊗ Chebyshev()

[codecov]

Codecov Report

Patch coverage: 19.23% and project coverage change: +0.16% 🎉

Comparison is base (27c3236) 27.41% compared to head (a4d9230) 27.58%.
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #541      +/-   ##
==========================================
+ Coverage   27.41%   27.58%   +0.16%     
==========================================
  Files          80       80              
  Lines        8363     8374      +11     
==========================================
+ Hits         2293     2310      +17     
+ Misses       6070     6064       -6     

Files Changed	Coverage Δ
src/Multivariate/ProductFun.jl	0.00% <0.00%> (ø)
src/eigen.jl	0.00% <0.00%> (ø)
src/Spaces/QuotientSpace.jl	3.95% <28.57%> (+0.50%)	⬆️
src/Multivariate/TensorSpace.jl	42.93% <100.00%> (+3.10%)	⬆️
src/Operators/banded/Conversion.jl	26.98% <100.00%> (+4.03%)	⬆️

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.