Add support for slash commands (under Feature Flag) (#6482)

* Add support for slash commands

* Update screenshots

* Rename module `slash` to `slashcommands`

* Rename `SlashCommand` to `SlashCommandService`

* Introduce MsgType in order to send text message with a different msgtype value.

* Format file and add parameter names, add default values and cleanup

* Add isSupported parameter to filter out unsupported yet commands.

* Slash commands: disable suggestions if the feature is disabled.

* Fix sending shrug command.

* Add missing test on SuggestionsProcessor

* Add tests on MessageComposerPresenter about slash command.

* Fix import ordering

* Add missing tests on CommandExecutor

* Add missing tests in MarkdownTextEditorStateTest

* Slash commands: Improve code when sending message with prefix.

* Slash commands: Add support for /unflip

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Co-authored-by: ElementBot <android@element.io>

features/messages/api/src/main/kotlin/io/element/android/features/messages/api/MessagesEntryPoint.kt

@@ -38,6 +38,7 @@ interface MessagesEntryPoint : FeatureEntryPoint {
         fun handlePermalinkClick(data: PermalinkData, pushToBackstack: Boolean)
         fun forwardEvent(eventId: EventId, fromPinnedEvents: Boolean)
         fun navigateToRoom(roomId: RoomId)
+        fun navigateToDeveloperSettings()
     }
 
     data class Params(val initialTarget: InitialTarget) : NodeInputs