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

[bmarty]

Type of change

• Feature
• 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
• 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 #8770.
What is blocking this PR?

[ganfra]

@bmarty Why are u doing that?
As it uses the CharSequence from the editor, it'll break the needsSendButtonVisibilityUpdate as currentComposerText will always be equals to action.text.
Reverting the change still allow to keep formatting when switching mode as far as I see.

[bmarty]

You're right, it is a mistake to change this. Reverted in 2395d72