[TASK] Refactor misleading method name

Purpose of the initialize() method in the AbstractAction class is the
initialization of a handle. It is not intended to be used for generally
initializing classes derived from AbstractAction.

By refactoring the method name, the method's purpose will be indicated
more clearer.

Change-Id: I1603090e4dfccb5b57da4fa9c3792ec73647c524
Resolves: #51396
Releases: 6.2
Reviewed-on: https://review.typo3.org/23364
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn