* Use getAttribute instead of dataset, in case SVG node APIs are unusual
* Use pointer-events instead of fill
* Use elementFromPoint instead of elementsFromPoint
* Move TextSourceRange static functions to DocumentUtil
getWritingMode is also simplified
* Update Google Docs range to be empty to match other range sources
* Rename imposterContainer to imposterElement
* Add static creation functions
* Add static creation function
* Remove unused collapse function
* Don't select imposter elements
* Refactor setEndOffset
* Adjust argument order for setEndOffset
* Update TextSourceRange constructor
* Remove unused isConnected
* Cache rects
* Fix test
* Remove unused getRect
* Revert "Fix test"
* Remove cachedRect
* Use the source element rect to handle scroll differences
* Writing mode update
* Remove _cachedRects update
This shouldn't be necessary as the imposter is usually detached
almost immediately after scanning, giving no time for the window
to be resized or scrolled.
