Edit label and tooltip for Preserve Shape setting (1.4.x)

For 1.4.x only. Follow-up to !6635 (merged)

The label and tooltip for the Preserve Shapes setting is misleading. Users expressed confusion when updating from 1.2.x.

@Moini in the linked MR:

How about: 'Use automatic corner detection when deleting nodes' - and a description like 'When active, Inkscape will try to detect whether the deleted node is a sharp corner. If it is a sharp corner, the node will be deleted, and the adjacent handles will stay unchanged. When it is not a sharp corner, the adjacent handles will be adjusted to preserve the shape. When inactive, Inkscape will always try to preserve the shape, like in Inkscape 1.2 and earlier.'

This is a variation of that copy.