better suggestions for builtin::trim equivalence (Resolves #23212)

[Grinnz]

There isn't really a reason to recommend a specific trim alternative anymore, instead we can recommend builtin::compat as a general solution for alternatives. Also suggest a better equivalent statement to the trim function. As suggested in #23212

Resolves #23212

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• This set of changes does not require a perldelta entry.

[tonycoz]

Fixes #23212 (to enable automatically closing that ticket)

GH wants specific wording in specific places, the "Fixes" doesn't appear to work in the subject, when it does work you get something like:

to the right (from #23204), while as I write this I see:

on this ticket

[khwilliamson]

@Grinnz Please do cd t; ./perl -I../lib porting/podcheck.t --regen and commit the changes, and repush