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>

appconfig/src/main/kotlin/io/element/android/appconfig/MessageComposerConfig.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2024 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.element.android.appconfig
+
+object MessageComposerConfig {
+    /**
+     * Enable the rich text editing in the composer.
+     */
+    const val ENABLE_RICH_TEXT_EDITING = true
+}