馃崚 kcms/notifications: Fix delegate's minimum size
The RowLayout within the delegate will not shrink below its content's implicit width, even when it overflows the external width constraint.
We can use some Layout properties in a creative way to reduce this, so that the TextField can shrink but keeps its regular size when the space available is wider.
BUG: 481433 FIXED-IN: 6.0
(cherry picked from commit 761eb760)