Allow bounding boxes transforms to *not* clamp

[NicolasHug]

Currently, all transforms that may potentially operate on a bounding box will automatically clamp that bounding box to its corresponding image dimensions. We've had feature requests in #7319 (comment) to allow for a non-clamping behaviour.

To preserve BC this could be enabled from a new parameter in all bbox-aware transforms. There might be alternative solutions (like a global flag, although pretty implicit), I haven't thought about it too much yet.