Add a PurpleRequestField:valid property and is_valid vfunc
* Add a `PurpleRequestField:valid` property and `is_valid` vfunc.
* Add a `GDestroyNotify` parameter for the validator data, and document the callback.
* Correct the property notification in `purple_request_field_bool_set_value`.
Testing Done:
Compiled and ran `ninja test`
Reviewed at https://reviews.imfreedom.org/r/2346/
# SOME DESCRIPTIVE TITLE.
# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
# This file is distributed under the same license as the PACKAGE package.
#
# Translators:
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"Project-Id-Version: Pidgin\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2022-10-26 01:46-0500\n"
"PO-Revision-Date: 2017-09-19 19:26+0000\n"
"Last-Translator: Richard Laager <rlaager@wiktel.com>\n"