Build: Switch unstable projects from -Xjvm-default=all-compatibility to all

With #175, Elementa now
uses `-Xjvm-default=all`, so we no longer need to explicitly mark new
interfaces with `JvmDefaultWithoutCompatibility`.

We don't need to mark anything with `JvmDefaultWithCompatibility`
because both, `statev2` and `layoutdsl`, projects are still considered
unstable, so we don't care about their ABI changing.

(We were already using `all` in Elementa's build script, just not in
Essential's version of these projects, hence why this doesn't actually
modify the build script.)

Source-Commit: fb810b4ef95f641bd02d9493312c9743025b45b2

Author: Johni0702

unstable/statev2/src/main/kotlin/gg/essential/elementa/unstable/state/v2/state.kt

@@ -205,7 +205,6 @@ interface ReferenceHolder {
  */
 
 /** A [State] with a value that can be changed via [set] */
-@JvmDefaultWithoutCompatibility
 interface MutableState<T> : State<T> {
   /**
    * Update the value of this State object.