Qt: Switch Qt5 to use KDE's Qt patch collection

From [1]
    What's this?

	This is a set of git repositories based on the last public
	commits available for Qt 5.15 branches with a curated collection
	of patches on top to ensure open source products can be used
	comfortably until users transition to their Qt 6-based ports.

    Which patches does it include?

	This collection of patches includes patches that fix at least
	one of the following:

	    * Security issues
	    * Crashes
	    * Functional defects

	We only include patches that have been approved upstream in the
	Qt project. If a patch cannot be merged upstream for technical
	reasons (e.g. the class no longer exists), it can also be
	merged.

	The patches to merge will be decided based on their relevance
	towards Open Source products and their viability.

PR:		260548
Exp-run by:	antoine
Differential Revision:	https://reviews.freebsd.org/D33446

[1] https://community.kde.org/Qt5PatchCollection