Make sure the mouse cursor is out of the popup

Make sure the mouse cursor is out of the popup

The x coordinate is now taken from the scintilla caret position. However,
when performing ctrl+click, we have to distinguish two cases:

1. the click happens in the second half of a letter - in this case the caret
is placed behind the letter and the popup appears behind it - no problem

2. the click happens in the first part of a letter - caret is placed before
the letter and the popup appears before the position where the click
happened - this means that the mouse cursor is above the popup which causes
that the mouse cursor highlights the item at the position of the cursor
instead of having the first item in the menu highlighted.

The patch calculates offset between caret and the mouse click event
position and uses this value to adjust the popup positioning so it's
outside the mouse cursor.