perlfunc: document return behavior of require

[Grinnz]

Resolves #23996

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

[Grinnz]

I added the line return 1 if $feature_module_true_enabled_in_file; in the "equivalent pseudocode" which hopefully conveys the intent of how the module_true feature affects the return value, but I'm not sure whether we want to indicate that as the behavior or whether it's accurate.