Editor: Improve keeping text selection between Visual and Text modes

[biskobe]

This patch is a continuation from #41962 / [41630].

What's new?

• Shortcodes should no longer break when selecting them from text mode and switching to Visual mode.
• No longer inserting empty paragraphs where the selection markers were, when going back and forth between Visual and Text modes.
• Live Preview shortcodes should now be properly selected in Text mode, when they were selected in Visual mode.

• Other general bug fixes and code improvements.

To test

1. Apply patch
2. Open the editor
3. Add content, click around, select things
4. Switch between modes
5. Try adding embeds
6. Try adding shortcodes

Look for JS errors in the console, weird behavior, etc.

Feedback

Please, add any feedback as a comment here or as a comment on the development PR, linked below.

[azaozz]

In 41645:

Editor: Improve keeping text selection when switching between Visual and Text modes.

Props biskobe.
See #42029.

[azaozz]

In 41646:

Editor: improve attaching a callback on editor init.

See #42029

[azaozz]

Still to do:

• There are couple of places where Underscore/Lodash is used, but it is not guaranteed it will be available. Refactor them to use similar helper methods in window.tinymce.
• Add support for disabling this from the editor settings?
• Perhaps use editor.on( 'beforeGetContent', ...) to always remove the selection marker. Can filter the editor DOM before serializing. This will remove it on switching editors, on saving, and when other plugins extract (some of) the content.

[azaozz]

In 41655:

Editor: pass the DOM library instance instead of a (fake) editor instance to getCursorMarkerSpan().

See #42029

[azaozz]

In 41656:

Editor: Use editor.$ to improve removeSelectionMarker().

See #42029

[jbpaul17]

Converting to task per the 4.9 bug scrub earlier today.

[obenland]

@iseulde Could you check if this needs any more work please?

[iseulde]

@obenland Sorry for the late reply. Will check tomorrow morning!

[iseulde]

From ​https://wordpress.slack.com/archives/C02RQBWTW/p1509034012000623 it seems that this ticket can be closed with all issues addressed. If there's anything else left, let's open new tickets for it.

[westonruter]

In 42183:

Editor: Improve scrolling behavior and prevent autosave logic from causing dirty state when just switching between Visual and Text tabs.

Props pento.
See #41962, #42029.
Fixes #42530 for trunk.

[westonruter]

In 42184:

Editor: Improve scrolling behavior and prevent autosave logic from causing dirty state when just switching between Visual and Text tabs.

Props pento.
See #41962, #42029.
Fixes #42530 for 4.9.

[westonruter]

In 42191:

Editor: Disable wp_keep_scroll_position in IE11 since buggy; fix matches polyfill conflict with ME.js by doing runtime feature detection in context window.

Props westonruter, SergeyBiryukov, Clorith for testing.
See #41962, #42029.
Fixes #42553 for trunk.

[westonruter]

In 42192:

Editor: Disable wp_keep_scroll_position in IE11 since buggy; fix matches polyfill conflict with ME.js by doing runtime feature detection in context window.

Props westonruter, SergeyBiryukov, Clorith for testing.
See #41962, #42029.
Fixes #42553 for 4.9.