Extract MessageComposerContext class from MessageComposerPresenter (#876)

When sending "Composer" analytics from screens other than the composer's (e.g. send location from map) we need to know the composer's mode in order to properly fill the analytics event. `MessageComposerContext` hoists this state so that other presenters can also read it.

Related to:
https://github.com/vector-im/element-meta/issues/1674
https://github.com/vector-im/element-meta/issues/1682

libraries/textcomposer/src/main/kotlin/io/element/android/libraries/textcomposer/MessageComposerMode.kt

@@ -51,4 +51,13 @@ sealed interface MessageComposerMode : Parcelable {
             is Quote -> eventId
             is Reply -> eventId
         }
+
+    val isEditing: Boolean
+        get() = this is Edit
+
+    val isReply: Boolean
+        get() = this is Reply
+
+    val inThread: Boolean
+        get() = false // TODO
 }