Disable location sharing when no MapTiler config is available

LocationService now exposes the MapTiler config to use: the one provided by the
homeserver takes precedence over the build time one, and null means that no map
provider is configured. It is now session scoped, and isServiceAvailable()
returns a StateFlow derived from this config.

When no config is available:
- the location sharing option is hidden from the composer, and location events
  cannot be opened in the location viewer;
- the "Location sharing" entry is hidden from the settings;
- location events in the timeline render a placeholder, without performing any
  request to MapTiler.

The show and share location screens now get the config from LocationService
rather than fetching the homeserver config by themselves.

Closes element-hq/element-android-enterprise#69

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/MessagesFlowNode.kt

@@ -776,7 +776,7 @@ class MessagesFlowNode(
                             assetType = event.content.assetType,
                         )
                     }
-                    NavTarget.LocationViewer(mode = mode).takeIf { locationService.isServiceAvailable() }
+                    NavTarget.LocationViewer(mode = mode).takeIf { locationService.isServiceAvailable().value }
                 } else {
                     displayVulkanNotSupportedError = true
                     null

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/messagecomposer/MessageComposerPresenter.kt

@@ -184,10 +184,7 @@ class MessageComposerPresenter(
 
         val cameraPermissionState = cameraPermissionPresenter.present()
 
-        val canShareLocation = remember { mutableStateOf(false) }
-        LaunchedEffect(Unit) {
-            canShareLocation.value = locationService.isServiceAvailable()
-        }
+        val canShareLocation by remember { locationService.isServiceAvailable() }.collectAsState()
 
         val isSendGalleryMessagesEnabled by featureFlagService.isFeatureEnabledFlow(FeatureFlags.SendGalleryMessages)
             .collectAsState(initial = false)
@@ -431,7 +428,7 @@ class MessageComposerPresenter(
             isInThreadTimeline = isInThread,
             showAttachmentSourcePicker = showAttachmentSourcePicker,
             showTextFormatting = showTextFormatting,
-            canShareLocation = canShareLocation.value,
+            canShareLocation = canShareLocation,
             suggestions = suggestions.toImmutableList(),
             resolveMentionDisplay = resolveMentionDisplay,
             resolveAtRoomMentionDisplay = resolveAtRoomMentionDisplay,