Make Matrix cntr work for structured matrices for zero(T) !isa T

[dkarrasch]

This fixes #44615 (comment). At the same time, it extends the Matrix constructors to other structured matrices whose eltype T has the property !isa(zero(T), T). Before #44615, Matrix(::Diagonal) was defined in terms of diagm, which handled the eltype promotion correctly. Matrix(::BiTriSym), however, was defined manually without correctly handling type promotion.

Fixes jump-dev/JuMP.jl#2930.

[dkarrasch]

@nanosoldier runtests(["JuMP"], vs = ":master")

[blegat]

Thanks! You can find here a list of assumptions commonly made and types for which it doesn't hold: jump-dev/MutableArithmetics.jl#47

[dkarrasch]

Aha, I realize you made a more complete proposal in #36256. Currently, none of the Matrix methods touched here works for eltypes T that don't have zero(T) defined. So this PR here fixes the issue, and puts BiTriSym to the same level as Diagonal. So shall we take this one and continue the discussion in #36256? Or should I cut down a bit and make the fix only for Diagonal?

[nanosoldier]

Your package evaluation job has completed - no new issues were detected. A full report can be found here.

[blegat]

shall we take this one and continue the discussion in #36256? Or should I cut down a bit and make the fix only for Diagonal?

Please leave this one as it is. I'll happily rebase #36256 once this one is merged.