Maintain selection and composition during updateText()

[dandclark]

Make the following changes to keep the selection and composition in a consistent state after updateText()/updateSelection() calls.

• For each selection bondary point, updateText() sets the boundary point to boundaryPoint + text.length - (rangeEnd - rangeStart) when boundaryPoint >= rangeEnd, or to rangeStart + text.length when boundaryPoint > rangeStart && boundaryPoint< rangeEnd.
• When a composition is active during an updateText() call,
  • If the updated range does not overlap with the composed range, move the composition position in the same way as for selection.
  • If it does overlap, abort the composition.
• When a composition is active when updateSelection() is called with a selection that differs from the current selection, abort the composition.

Resolves #111.

For normative changes, the following tasks have been completed:

• Editing WG resolution on the proposed changes, with at least two implementers participating and not objecting:

  • WebKit
  • Chromium
  • Gecko

• For browsers that are shipping the feature, implementation bugs are filed for the proposed changes (link to bug, or write "Not Implementing"):

  • WebKit (https://bugs.webkit.org/show_bug.cgi?id=)
  • Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
  • Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)

[marijnh]

Thanks. These changes would solve the issues I've been running into.