[BUGFIX] Use more intuitive shortcut to open the live search

The UX team discusses internally whether the existing shortcut to open
the live search (Shift+Shift) introduced in #98348 is counter-intuitive
for regular editors or not.

Common sense seems to be Ctrl/Cmd+K to open the search in several
applications and websites (Discord, Slack, and even in Chrome), so the
keyboard shortcut should be changed.

If any modal is already open, the new keystroke is not caught and any
default browser behavior is kept.

Resolves: #98467
Related: #98348
Releases: main
Change-Id: I6e4a08030f88ebee1cc0e6f944786e1defb30ea4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75890


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Froemken <froemken@gmail.com>
Tested-by: Frank Nägler <frank.naegler@typo3.com>
Tested-by: Annett Jähnichen <mcmietz@web.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Stefan Froemken <froemken@gmail.com>
Reviewed-by: Frank Nägler <frank.naegler@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>