Better handling of text composition

[nightwing]

https://rawgit.com/ajaxorg/ace/master/kitchen-sink.html

Overview

Textinput stores selection and value of textarea
After input event, sendtext checks the difference from the last value, and detects what change is needed to get from old value to the new one.
The normal case of inserting text goes through the old codepath, and there is a new handler for the case when selection needs to be modified before or after the insertion.
textarea size is set to 1px (0 on ie to hide the blinking cursor) comment in monaco was saying that there is an issue with setting it 0 on all browsers.
Font size is set to 1px on desktop, to make sure the text in textarea doesn't change the position of ime popup much, and inherit on mobile to not trigger zoom on focus
After endOperation events value of textarea is set to the current line (two lines around the cursor for multiline selections) this allows screen readers to work the same way as in textarea, and also helps with mobile keyboards that do not fire proper events
For the composition there are two modes
On chrome and firefox we set textarea value to "", make textarea visible, and add a placeholder token under it, this allows the native underline to be visible, which has information about word boundaries
on other browsers we keep textarea hidden, insert text into the document and add a marker for the underline (this is needed because on mobile all text input goes through composition events, and on ie setting value to "" from composition start doesn't work)

Testing

Manually tested windows, linux, mac with combinations of ie11, chrome, firefox, safari, for japanese and korean ime
android: chrome and firefox with gboard, samsung keyboard, swiftkey, hackers keyboard

[adamjimenez]

This seems to fix #2038 and a bunch others.
❤️ @nightwing

[vanillajonathan]

This works great on Android! <3

[adamjimenez]

The Live autocompletion in the kitchen sink demo doesn't show on Chrome for Android. It does show on the master branch
Backspacing a new line after pressing enter takes a few presses before it deletes.
Backspacing a line seems to mess up the virtual keyboard completions.

[codecov]

Codecov Report

Merging #3635 into master will increase coverage by 0.87%.
The diff coverage is 96.29%.

@@            Coverage Diff             @@
##           master    #3635      +/-   ##
==========================================
+ Coverage   67.21%   68.09%   +0.87%     
==========================================
  Files         483      485       +2     
  Lines       47927    48191     +264     
  Branches     9106     9138      +32     
==========================================
+ Hits        32214    32814     +600     
+ Misses      15713    15377     -336

Impacted Files	Coverage Δ
lib/ace/lib/useragent.js	16.12% <0%> (-1.12%)	⬇️
lib/ace/mouse/mouse_handler.js	80.76% <100%> (+0.45%)	⬆️
lib/ace/keyboard/vim.js	86.74% <100%> (+2.8%)	⬆️
lib/ace/editor.js	77.44% <91.42%> (+0.43%)	⬆️
lib/ace/keyboard/textinput.js	78.57% <95.52%> (+40.38%)	⬆️
lib/ace/keyboard/vim_ace_test.js	96.25% <96.25%> (ø)
lib/ace/virtual_renderer.js	73.9% <98.21%> (+4.29%)	⬆️
lib/ace/keyboard/textinput_test.js	99.16% <99.16%> (ø)
... and 12 more

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[nightwing]

Thanks for testing! The new version should fix issues with autocompletion and backspace.
And all the issues from https://github.com/ajaxorg/ace/issues?q=project:ajaxorg/ace/1