replace! dispatches on ::Function

[jariji]

I'm reporting functions that dispatch on types like ::Function. replace! is one of these.

replace!(A, old_new::Pair...; [count::Integer])
replace!(new::Function, A; [count::Integer])

I propose replacewith! a a new name for the one that takes a callable, by analogy to mergewith!, whose introduction is justified here:

With multiple dispatch, just as the meaning of a function is important to get consistent, it's also important to get the meanings of the argument slots consistent when possible. It's not ideal for a function to treat an argument in a fundamentally different way based on its type: e.g. "if this is a Function, then call it on pairs of values, otherwise assume it's a container providing the values to use".

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Related issue: #49085