Restore the URL when DolphinSearchBox is cleared

Restore the URL when DolphinSearchBox is cleared

Currently, the URL navigator is not updated when the search box is cleared. This MR restores the URL, by closing and reopening the box.

The call for emitting closeRequest() on pressing Esc has been replaced with emitCloseRequest(). The wait duration before starting a search has been reduced to 500ms to increase responsiveness.

Also, the bugfix for BUG: 423328 is slightly incorrect and causes the search term to not be displayed when opening a saved search for the first time. As a better solution for this bug, DolphinSearchBox::setText() now updates the text only if the text has changed.

BUG: 473775