[BUGFIX] Compact clear cache button when one item exists

This change makes the clear cache toolbar item dynamically
either render a drop-down as it did before, or render a single
link directly if there is only a single clear cache action.

If any hooks or permissions add additional items the drop-
down is rendered again.

Change-Id: Iadac80405bf1152a849d4d4269a9bc0728b0b459
Releases: master
Resolves: #78656
Reviewed-on: https://review.typo3.org/50594


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Philipp Gampe <philipp.gampe@typo3.org>
Tested-by: Philipp Gampe <philipp.gampe@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>