Show a prompt to reinvite other party in a DM

If you are looking at a DM where the other party has left then
when you focus the composer for the first time we'll show a
dialog asking if you want to reinvite the other party.

Closes #590

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/room/MatrixRoom.kt

@@ -44,6 +44,7 @@ interface MatrixRoom : Closeable {
     val isEncrypted: Boolean
     val isDirect: Boolean
     val isPublic: Boolean
+    val activeMemberCount: Long
     val joinedMemberCount: Long
 
     /**

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/room/RustMatrixRoom.kt

@@ -174,6 +174,9 @@ class RustMatrixRoom(
     override val joinedMemberCount: Long
         get() = innerRoom.joinedMembersCount().toLong()
 
+    override val activeMemberCount: Long
+        get() = innerRoom.activeMembersCount().toLong()
+
     override suspend fun updateMembers(): Result<Unit> = withContext(coroutineDispatchers.io) {
         val currentState = _membersStateFlow.value
         val currentMembers = currentState.roomMembers()

libraries/matrix/test/src/main/kotlin/io/element/android/libraries/matrix/test/room/FakeMatrixRoom.kt

@@ -53,6 +53,7 @@ class FakeMatrixRoom(
     override val isPublic: Boolean = true,
     override val isDirect: Boolean = false,
     override val joinedMemberCount: Long = 123L,
+    override val activeMemberCount: Long = 234L,
     private val matrixTimeline: MatrixTimeline = FakeMatrixTimeline(),
 ) : MatrixRoom {
 

libraries/matrix/test/src/main/kotlin/io/element/android/libraries/matrix/test/room/RoomMemberFixture.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2023 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.libraries.matrix.test.room
+
+import io.element.android.libraries.matrix.api.core.UserId
+import io.element.android.libraries.matrix.api.room.RoomMember
+import io.element.android.libraries.matrix.api.room.RoomMembershipState
+
+fun aRoomMember(
+    userId: UserId = UserId("@alice:server.org"),
+    displayName: String? = null,
+    avatarUrl: String? = null,
+    membership: RoomMembershipState = RoomMembershipState.JOIN,
+    isNameAmbiguous: Boolean = false,
+    powerLevel: Long = 0L,
+    normalizedPowerLevel: Long = 0L,
+    isIgnored: Boolean = false,
+) = RoomMember(
+    userId = userId,
+    displayName = displayName,
+    avatarUrl = avatarUrl,
+    membership = membership,
+    isNameAmbiguous = isNameAmbiguous,
+    powerLevel = powerLevel,
+    normalizedPowerLevel = normalizedPowerLevel,
+    isIgnored = isIgnored,
+)

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

@@ -53,6 +53,7 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.focus.FocusRequester
 import androidx.compose.ui.focus.focusRequester
+import androidx.compose.ui.focus.onFocusEvent
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.ColorFilter
 import androidx.compose.ui.graphics.SolidColor
@@ -93,6 +94,7 @@ fun TextComposer(
     onResetComposerMode: () -> Unit = {},
     onComposerTextChange: (CharSequence) -> Unit = {},
     onAddAttachment: () -> Unit = {},
+    onFocusChanged: (Boolean) -> Unit = {},
 ) {
     val text = composerText.orEmpty()
     Row(
@@ -129,7 +131,8 @@ fun TextComposer(
                     modifier = Modifier
                         .fillMaxWidth()
                         .heightIn(min = minHeight)
-                        .focusRequester(focusRequester),
+                        .focusRequester(focusRequester)
+                        .onFocusEvent { onFocusChanged(it.hasFocus) },
                     value = text,
                     onValueChange = { onComposerTextChange(it) },
                     onTextLayout = {