Change inline-edit mouse input handling

This changes the mouse click handler for input fields to the
following logic:

* If the cursor isn't already in the input field:
  * On mouse over displays the POINTER_REFHAND
  * A left click selects the whole text of the field and therefore
    moves the cursor to the end of the field
  * Same for the right click. Additionally it opens the popup menu

* If the cursor is already in the input field:
  * As for normal text, the left click removes the selection and
    moves the cursor to the click location.
  * Right click keeps any selection and opens the popup

In contrast to normal text editing, a double click still opens
"Edit fields" dialog, instead of the word selection.

Change-Id: Ie7a50b34fe625358426d18eaec2e833f36702528
Reviewed-on: https://gerrit.libreoffice.org/10836
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>