Qt supports some complex foreground brushes which we cannot
express using normal CSS, so we introduce a Qt-specific property
for this. We already had some support for background gradients
in widget style sheets, but this expands support to foreground
brushes of text when converting a QTextDocument from and to HTML.
It also adds an optional "coordinatemode" attribute to the
gradient functions so that this can be faithfully restored from HTML.
Task-number: QTBUG-123357
Change-Id: I3d6dd828f68272995c8525bec5a7b421fdbed670
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
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