Editing: Replace snackbar with compact notice when switching editor mode

[ovitrif]

Fixes #11819

It was brought to our attention that some users find the snackbar appearing at the bottom of the screen when the editor mode is switched to HTML annoying because they cannot edit the last lines before it disappears.

This PR replaces the snackbar at the bottom with a compact notice shown at the top of the screen, below the main top bar of the app (see screenshots).
This solution was suggested after a discussion in the issue where we also explored the option of not showing any notice.

The snackbar is now replaced with the notice in both cases:

• When we switch the editor to HTML mode
• When we switch the editor to Visual Mode

To test

1. From My Site press the Posts button or scroll down and select Blog Posts from the list
2. In post cards mode press the More button / In post list mode press the dots at the right of the post
3. Press Edit (first button)
4. In the editor, Tap the 3 dots in the upper right corner
5. Tap HTML Mode (3rd button)
6. Verify that a compact notice appears at the top of the editor, and no snackbar is shown
7. Tap again the 3 dots in the upper right corner
8. Tap Visual Mode (3rd button)
9. Verify that a compact notice appears at the top of the editor, and no snackbar is shown

Screenshots

Switching to HTML mode

Before	After

Switching to Visual mode

Before	After

GIF Preview

Notice when switching editor mode

Regression Notes

1. Potential unintended areas of impact
   None, because the snackbar that is replaced was only shown when switching editor mode, and now we show a notice instead.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Manual testing.

3. What automated tests I added (or what prevented me from doing so)
   None, since this change does not warrant such tests.

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[antonis]

Great work @ovitrif 👍
I tested this on an Pixel 5 (Android 12) and everything works as expected 🎉
The code changes are consistent and LGTM ✅

[ovitrif]

Thank you @antonis for the review!
Feels great to be able to contribute 😇

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APKs:

• Jetpack-pr-15589-build-117098.apk
• WordPress-pr-15589-build-117098.apk