Fix popup position if popup is triggered from within an offsetParent element (#6887)

* Fix popup location for tables

This commit introduces the `popupAbsCoords` option to the $button widget
and implements an absolut coordinate format.

Coordinates for popups are stored in the format `(x,y,w,h)`. These
coordinates are relative to the offset parent of the element that
defines the popup.

This commits adds a second format `@(x,y,w,h)`. Coordinates specified in
this format a relative to the pages root element.

The `popupAbsCoords` option of the $button widget enables the use of
this coordinates.

* Unify the declaration of the RegEx for parsing the popup-position

The regular expression was declared in three locations with the same
content. This commit supplies a new function `parseCoordinates` in
`popup.js`. This function returns the parsed coordinates and understands
the classic/absolute coordinates.

This function is used in `reveal.js` and `action-popup.js` to parse the
coordinates.

* Add documentation for coordinate systems

* Consolidate creating coordinate strings

The Popup object now contains a `buildCoordinates` method that can be
used to build coordinate strings. It takes an "enum" for the coordinate-
system to use. This makes everything easily extensible and prevents the
use of magic values.

* Add tests for `parseCoordinates` and `buildCoordinates`

* Add `tv-popup-abs-coords` to `collectDOMVariables`

This will make the absolute coordinates available for the
`DraggableWidget` and the `EventCatcherWidget`.

* Add documentation for the `tv-popup-abs-coords`

... to the `DraggableWidget` and the `EventCatcherWidget`.

plugins/tiddlywiki/dynannotate/modules/dynannotate.js

@@ -191,7 +191,7 @@ DynannotateWidget.prototype.applyAnnotations = function() {
 				"tv-selection-posy": (bounds.top).toString(),
 				"tv-selection-width": (bounds.width).toString(),
 				"tv-selection-height": (bounds.height).toString(),
-				"tv-selection-coords": "(" + bounds.left + "," + bounds.top + "," + bounds.width + "," + bounds.height + ")"
+				"tv-selection-coords": $tw.popup.buildCoordinates($tw.popup.coordinatePrefix.csOffsetParent,bounds)
 			});
 			if(self.hasAttribute("popup")) {
 				$tw.popup.triggerPopup({