Instead of requiring users to enable the core c++ plugin 'Coordinate Capture'
in order to copy coordinates for a map point, instead add this functionality
to a map canvas right click context menu.
Now, when compatible map tools are activated (pan, zoom, select by rect), right clicking
on the canvas shows a context menu with a "Copy Coordinate" submenu. The
submenu shows options for copying the coordinate in the map CRS, WGS84 or
a custom preset CRS.
Also adds API to allow 3rd party QgsMapTool subclasses to implement their own
context menus which include this Copy Coordinate action.
operation is in progress
This causes the status bar coordinates widget to show nonsense coordinates
during the pan operation. The cursor world position ISN'T changing during
a pan operation, it stuck to a fixed location!