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/preferences/impl/build.gradle.kts

@@ -75,6 +75,7 @@ dependencies {
     implementation(projects.features.analytics.api)
     implementation(projects.features.enterprise.api)
     implementation(projects.features.licenses.api)
+    implementation(projects.features.location.api)
     implementation(projects.features.logout.api)
     implementation(projects.features.deactivation.api)
     implementation(projects.features.invite.api)
@@ -109,6 +110,7 @@ dependencies {
     testImplementation(projects.features.enterprise.test)
     testImplementation(projects.features.invite.test)
     testImplementation(projects.features.licenses.test)
+    testImplementation(projects.features.location.test)
     testImplementation(projects.features.lockscreen.test)
     testImplementation(projects.features.logout.test)
     testImplementation(projects.libraries.indicator.test)