Plain text editor implementation based on markdown input (#2840)

* Add plain text editor based on markdown input
- Fix autofocus of message composer.
- Remove `Message` data class, fetch the details in `MessagesPresenter` instead.
- Remove `enable rich text` option from advanced settings, set it as a build configuration instead.
* Fix MentionSpanProvider
* Bump RTE library to released `v2.37.3`

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Co-authored-by: ElementBot <benoitm+elementbot@element.io>

.maestro/tests/roomList/timeline/messages/text.yaml

@@ -2,7 +2,7 @@ appId: ${MAESTRO_APP_ID}
 ---
 - takeScreenshot: build/maestro/510-Timeline
 - tapOn:
-    id: "rich_text_editor"
+    id: "text_editor"
 - inputText: "Hello world!"
 - tapOn: "Send"
 - hideKeyboard

.maestro/tests/settings/settings.yaml

@@ -34,7 +34,7 @@ appId: ${MAESTRO_APP_ID}
 
 - tapOn:
     text: "Advanced settings"
-- assertVisible: "Rich text editor"
+- assertVisible: "View source"
 - back
 
 - tapOn: