[WIP] Textarea based composer input

[t3chguy]

Fixes element-hq/element-web#4861
Signed-off-by: Michael Telatynski 7t3chguy@gmail.com

[ara4n]

I'm worried that the maintenance burden of the overlapping functionality between the draft & textarea-based composer is going to be a pain - I was expecting more to be factored out between the two, particularly: typing notifs, history management, clipboard pasting, processing slash commands. Otherwise the two are just going to spend their lives drifting out of sync with one another.

It otherwise looks good though :)

[dbkr]

Echoing what @ara4n says about code duplication - I think this will be too much of a burden without factoring out the common functionality.

[lukebarnard1]

@t3chguy are you likely to have another crack at doing this in a way that factors out functionality between both composers?

[lukebarnard1]

FTR this looks like it will be usurped by move to Slate from Draft.js anyway.

[t3chguy]

I don't think this is superseded but will definitely be broken by;
Draft.js and Slate both use a contenteditable div which doesn't play very well with extensions which people like to use in their browsers to improve their editing experience, and other fun stuff like pop-out editors, which is why this PR was even a thing.

[lukebarnard1]

Fair enough, @t3chguy. "Usurped" was probably the wrong word, my bad.

I can see us definitely wanting to support an "insert your favourite editor here" functionality, even with Slate.