[ENHANCEMENT] Ignore extraneous dimension names in qr/svd

[mtfishman]

A common code pattern in ITensors.jl is analogous to the following:

using NamedDimsArrays: nameddims
a = nameddims(randn(2, 2), ("i", "j"))
b = nameddims(randn(2, 2), ("j", "k"))
q, r = qr(b, dimnames(a))

This fails right now because qr(::AbstractNamedDimsArray, codomain_names) is strict about the names that are input as the codomain names in the factorization, and dimnames(a) contains the name "i" which isn't a dimension name of b.

One can do:

q, r = qr(b, intersect(dimnames(b), dimnames(a)))

but that is a bit annoying to write which is why we automated it in ITensors.jl. We could have a keyword argument that toggles between the two:

 # errors
q, r = qr(b, intersect(dimnames(b), dimnames(a)); strict=true)

# no error, equaivalent to `qr(b, intersect(dimnames(b), dimnames(a)))`, probably the default
q, r = qr(b, dimnames(a); strict=false)

Additionally, I think passing both the codomain and domain names should be strict, i.e.:

q, r = qr(b, dimnames(a), ("j",)) # errors
q, r = qr(b, ("i",), ("j",)) # works
q, r = qr(b, intersect(dimnames(b), dimnames(a)), setdiff(dimnames(b), dimnames(a))) # works

[mtfishman]

Note that qr(::AbstractNamedDimsArray, ...)/svd(::AbstractNamedDimsArray, ...) forward to TensorAlgebra.qr/TensorAlgebra.svd and this discussion is relevant for that package as well.