…ing editors

FIX: Improve touch tap-selection on line wrapping boundaries.

Issue codemirror/dev#1677

FIX: Make `drawSelection` draw our own selection handles on iOS.

Issue codemirror/dev#1538

…ned by Safari

FIX: Fix an issue where `posAtCoords`, when querying line wrapping points,
got confused by extra empty client rectangles produced by Safari.

Closes codemirror/dev#1679

FEATURE: `WidgetType.updateDOM` is now called with the previous widget value
as third argument.

See https://discuss.codemirror.net/t/accessing-other-instance-in-widgettype-updatedom/9693

With `this` TypeScript understands that it's the same type as the subclass.

FIX: Fix a bug that caused Shift-Enter/Backspace/Delete on iOS to lose the shift
modifier when delivered to key event handlers.

Closes codemirror/dev#1682

FIX: Fix an issue where `EditorView.moveVertically` could move to the wrong place
in wrapped lines with a large line height.

Issue codemirror/dev#1681

FIX: Make sure the selection head associativity is properly set for mouse
selections made with shift held down.