[orca-list] Text event and clipboard changes committed to master

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

I just committed a pretty significant change to Orca master. It's both a
refactor of text event handling and some new features. In particular:

* Present copy, cut, paste, undo, redo, selection deletion, and
  selection restoration
* Improve presentation of selected content in Gecko
* Stop checking for text selection in places where it doesn't make
  sense for performance.

Please note, this is the initial commit of these changes. There are
still some issues with LibreOffice and Gecko. In the case of
LibreOffice, most of the issues seem to be the result of bugs in
LibreOffice. I need to confirm that, however. And if that's the case,
I'll file bugs against LibreOffice.

With Gecko content, the biggest known issue is when text selection is in
a table. This is something I'm still working on and (so far) the issues
do not seem to be Gecko bugs; I just need to add the support. Also, it's
worth noting that Orca does not control the caret when you are selecting
text; at that point, you're using Gecko's native caret navigation and
selection. Orca's just presenting the result. Orca-controlled text
selection remains on my to-do list.

All of this said, if you're in normal, non-table content (a series of
paragraphs, headings, list items, etc.), I think (and hope!) you'll find
text selection presentation has improved quite a bit. I also hope you
like the presentation of copy, cut, paste, etc.

Lastly, the usual reminder: The thing I'm most interested in hearing
about are regressions. If you are not sure if you have a regression, or
just stumbled across an existing bug, check out the commit prior to this
change and see if the problem is there too. While you test for
regressions and user experience, I'll keep tackling the remaining issues.

Thanks!
--joanie