Try to make all collections used in Compose code immutable (#1922)

* Try to make all collections used in Compose code immutable.

Mark sealed interfaces as `@Immutable` too

* Add gradle code to check the compose compiler reports

* Fix some more unstable classes

libraries/matrix/test/build.gradle.kts

@@ -28,4 +28,5 @@ dependencies {
     api(libs.coroutines.core)
     implementation(libs.coroutines.test)
     implementation(projects.tests.testutils)
+    implementation(libs.kotlinx.collections.immutable)
 }