Previously, in the 'Keys' preference page, binding a key to the
'Clear Console' command, would only affect process consoles, such as
the 'Run as -> Java Application' console.

It did not work in any other consoles.

Solution:
* Move the 'org.eclipse.debug.ui.commands.console.clear from
  org.eclipse.debug.ui to org.eclipse.ui.console.
  The ID is kept stable to not break any existing key bindings.
  The Category is changed to org.eclipse.ui.category.edit.

* Set action defintion ID for the clear command to also show an active
  key binding in the context menu.

* Enable the 'clear console' handler also in in the generic
  TextConsolePage.