Multiple Issues with bounding box in QtSvg

Filters change the bounding box of an SVG element in most reference implementations such as Chrome and Firefox. This is important because applying another filter on top (made possible by putting the element into a group element and applying the filter to the group element) will then lead to different results.

Another issue with the bounding box affects the fix for QTBUG-122310. Here we need a buffer that contains all graphic elements of the group, including markers. However, markers are not part of the bounding box (as used in filters) in reference implementations such as Chrome and Firefox.

We probably need two functions, one including filters, another one including filters and markers. The current implementation ignores both.

This is a bug that was discovered in a users svg:
https://github.com/linuxdeepin/deepin-icon-theme/blob/master/bloom/apps/96/deepin-image-viewer.svg
https://github.com/linuxdeepin/deepin-icon-theme/blob/master/bloom/apps/96/deepin-screen-recorder.svg