Allow rank computation for QRPivoted matrices

[danilonumeroso]

Hi, this fixes JuliaLang/LinearAlgebra.jl#1052. I followed @stevengj's code suggestion which worked just fine and added tests in the related section.

Note: this is my first contribution so please feel free to point out any rookie mistakes I might have made!

[stevengj]

LGTM. Do you also want to tackle JuliaLang/LinearAlgebra.jl#1052? If nullspace and cond aren't addressed in this PR, which is fine, we should open a new issue for those after this PR is merged.

[stevengj]

Probably worth adding a NEWS.md entry.

Not sure where else it would be good to document this?

[danilonumeroso]

LGTM. Do you also want to tackle #53214 (comment)? If nullspace and cond aren't addressed in this PR, which is fine, we should open a new issue for those after this PR is merged.

Yes, I'd like to. I'm going to open a new issue for those and tackle it in a separate PR

Probably worth adding a NEWS.md entry.

Not sure where else it would be good to document this?

Done! Please tell me if I need to be more specific and/or there's any standard I should follow for NEWS.md entries