[FEATURE][cad] Implement "repeating" locking mode for constraints

When enabled, repeating locks are not automatically cleared when
a new point is added. They are handy when the same constraint
must be repeated for multiple points (eg adding vertices
which are always 50 meters apart)

(fix #12605)

Author: nyalldawson

images/images.qrc

@@ -581,6 +581,7 @@
         <file>themes/default/multieditChangedValues.svg</file>
         <file>themes/default/multieditMixedValues.svg</file>
         <file>themes/default/multieditSameValues.svg</file>
+        <file>themes/default/locked_repeating.svg</file>
     </qresource>
     <qresource prefix="/images/tips">
         <file alias="symbol_levels.png">qgis_tips/symbol_levels.png</file>