Selection Paste Enhancements

When pasting the selection, the cursor position should be changed to the location where the mouse is pointing when the middle mouse button is released not where the current text cursor is located.  The event received in the mouse release event handler contains the position of the mouse relative to the widget (in this case the edit box).

The mouse position is passed to the cursorForPosition() function of the QPlainTextEdit base class to obtain a text cursor for the this position.  The edit box text cursor is then set to this text cursor to move the cursor, so when the selection is pasted, the text will be inserted to where the mouse was pointing.

It is also nice to be able to paste the current selection using a key command.  The Control+Shift+Insert key sequence was chosen.  Shift+Insert is the key sequence is used to paste the contents of the clipboard.  A case was added to the key press event handler key code switch for the Insert key, which checks for the Control and Shift key modifiers.

Since middle mouse button and Control+Shift+Insert needed to do the same thing, a paste selection function was implemented from parts of the mouse release event handler, which gets the clipboard for the application, checks if the selection is supported, sets the text cursor position to the mouse location, gets the text for the selection and inserts the text.  The function returns true if the selection was pasted, and false if the selection is not supported.

Since the position is only set with the middle mouse button, the paste selection function contains a position argument, which defaults to a null point.  The text cursor is only set to this position when the position is not a null point.  Only the mouse release event handler passes the position of the mouse (from the event).

It was also noticed that the backspace key code check in the key press event handler was in the default section of the switch statement that handled the key sequences.  The backspace check was removed and a backspace key code case was added to the switch.

Next Work: Handling the pasting of text when there is current selection text in the edit box, where the inserted text will replace the selection.  This handling will need to detect how many if any lines needed to be reported as being deleted, before reporting the changed and inserted lines from the paste.

[commit addb4fd6eb] [commit 6af5c59191]