AbstractArrays in broadcast falls back to slow objectid when checking mightalias

[KristofferC]

See the comment at #25890 (comment). and e.g. JuliaArrays/UnsafeArrays.jl#3.

mightalias is undocumented but yet it is sorely needed to overload in case one wants to have good performance when broadcasting with custom arrays.
Otherwise, a fallback objectid function is called which is slow.

[KristofferC]

Ref #26237

[nsajko]

xref #51753