rich text: limit size of text object

rich text: limit size of text object

Origin: upstream, https://code.qt.io/cgit/qt/qtdeclarative.git/commit/?id=144ce34e846b3f73
 Backported to 5.15 by Dmitry Shachnev: validate allocation manually
 instead of using QImageIOHandler::allocateImage().
Last-Update: 2025-12-11

When we draw a text object, we need to store this in RAM
since the QTextObjectInterface is QPainter-based. This
could lead to over-allocation if the text object size
was set to be very large. We use the existing image IO
infrastructure for making sure allocations are within
reasonable (and configurable) limits.

Gbp-Pq: Name CVE-2025-12385-part2.patch