[BUGFIX] Fix automatic core updater

AbstractCoreUpdate redefines the $view member to be
a JsonView, but does not re-implement the parent methods
that rely on $view being an AbstractView.

Fix this by re-implementing the initializeHandle() method.
This method can be merged with the former initializeCoreUpdate(),
which wasn't called at all in most actions.

Resolves: #56865
Releases: 6.2
Change-Id: I85260a0e57e915ac941569cfbdde1f96cdaec5e6
Reviewed-on: https://review.typo3.org/28393
Reviewed-by: Philipp Gampe
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Markus Klein
Tested-by: Markus Klein