Fix Rich Text Editor issues: save formatted text in draft and keep formatting when switching between modes

[bmarty]

Type of change

• [ ] Feature
• [x] Bugfix
• [ ] Technical
• [ ] Other :

Content

• First commit: When using the RichTextEditor, store the formatted text into the Draft, to be able to restore it correctly.
• Second commit: Keep the formatted text into memory to be able to keep it when switching between composer modes.

Motivation and context

Avoid formatting loses.

Closes #7466

Screenshots / GIFs

Tests

• Enable the RichTextEditor

• Add some formatted content to the composer, and do not send the message

• go back to the room list

• open the room with the draft

• observe that the text is formatted as before.

• swipe a previous message to start replying to it

• observe that the formatting is not lost when doing that

• Disable the RichTextEditor

• observe that draft feature works like before (so no regression)

As a limitation, a draft saved with the RTE enabled can be restored a bit wildly once the RTE has been disabled. But I think this is an acceptable limitation. We may want to clear all the drafts when toggling the RTE, but user data will be lost.

Tested devices

• [ ] Physical
• [x] Emulator
• OS version(s):

Checklist

• [ ] Changes has been tested on an Android device or Android emulator with API 21
• [ ] UI change has been tested on both light and dark themes
• [ ] Accessibility has been taken into account. See https://github.com/element-hq/element-android/blob/develop/CONTRIBUTING.md#accessibility
• [ ] Pull request is based on the develop branch
• [ ] Pull request includes a new file under ./changelog.d. See https://github.com/element-hq/element-android/blob/develop/CONTRIBUTING.md#changelog
• [ ] Pull request includes screenshots or videos if containing UI changes
• [ ] Pull request includes a sign off
• [ ] You've made a self review of your PR
• [ ] If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[ganfra]

It looks like it's breaking some computation with the send button visibility... There is some scenarios where the send button never shows up. On develop I can't reproduce, but the send button is blinking when typing text (with RTE enabled).

[bmarty]

There is some scenarios where the send button never shows up

I cannot repro the issue of send button not visible. Can you be more precise about the scenario to repro please?

[giomfo]

It looks like it's breaking some computation with the send button visibility... There is some scenarios where the send button never shows up. On develop I can't reproduce, but the send button is blinking when typing text (with RTE enabled).

@ganfra what is the scenario where the send button disappears? about the blinking, I think this was fixed by https://github.com/element-hq/element-android/pull/8770. What is blocking this PR?