patch 9.1.1571: CmdlineChanged triggered to often

patch 9.1.1571: CmdlineChanged triggered to often

Problem:  The CmdlineChanged event was firing unnecessarily, even when
          the command line's content hadn't actually changed.

Solution: I've added a check to compare the command-line buffer's state
          before and after key processing. The `CmdlineChanged` event
          now only triggers if the buffer's contents are genuinely
          different (Girish Palya).

closes: #17803

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>