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/preferences/api/src/main/kotlin/io/element/android/features/preferences/api/PreferencesEntryPoint.kt

@@ -28,6 +28,9 @@ interface PreferencesEntryPoint : FeatureEntryPoint {
 
         @Parcelize
         data object NotificationTroubleshoot : InitialTarget
+
+        @Parcelize
+        data object DeveloperSettings : InitialTarget
     }
 
     data class Params(val initialElement: InitialTarget) : NodeInputs