Beef up TransposedView

[eggrobin]

(Note: we may want to have a more general and more powerful TransposedView in the future as the result of all Transpose (with conversions to the appropriate matrix types if actual transposition of the data is needed), but this is a rabbit hole for another day; for now this draft is good enough.)

Originally posted by @eggrobin in #3287 (comment)

[pleroy]

Also unify the operators in fixed_arrays and unbounded_arrays to avoid having each implementation twice.