Merge similar strings in REST API deprecated function/argument handlers

[SergeyBiryukov]

In rest_handle_deprecated_function(): '%1$s (since %2$s; use %3$s instead)'.
In rest_handle_deprecated_argument(): '%1$s (since %2$s; %3$s)'.

Unless I'm missing something, the latter could use the first string too.

[rmccue]

For _deprecated_function, the arguments are $file, $version, $replacement; for _deprecated_argument, they're instead $function, $version, $message. We have the different strings here because functions typically only have a replacement function string, whereas arguments have a sentence explaining it.

[ocean90]

34908.patch​ improves the docs and renames the third argument of rest_handle_deprecated_argument() to $message.

[SergeyBiryukov]

34908.patch​ looks good, but the translator comment should be updated as well.

I was confused by "3: new argument name" when translating the string.

[rachelbaker]

updated translator comment

[rachelbaker]

I updated the translation comment within rest_handle_deprecated_argument() for the $message argument in 34908.1.patch​. @ocean90 can you review?

[SergeyBiryukov]

Looks good.

[rachelbaker]

In 35845:

Docs: Better param descriptions and fix incorrect param name within REST API deprecated functions

rest_handle_deprecated_function: you get better parameter descriptions.
rest_handle_deprecated_argument: you get a corrected parameter name ($replacement->$message), appropriate i18n translation hints, and better parameter descriptions.

Props ocean90.
Fixes #34908