Fix corrupted and invalidly symlinked worlds crashing on level select (#10415)

src/main/java/net/minecraftforge/common/extensions/IForgeLevelSummary.java

@@ -0,0 +1,22 @@
+package net.minecraftforge.common.extensions;
+
+import net.minecraft.world.level.storage.LevelSummary;
+
+public interface IForgeLevelSummary {
+    private LevelSummary self() {
+        return (LevelSummary) this;
+    }
+
+    /**
+     * Checks if the Forge lifecycle of this level is experimental. This is used to render the experimental warning
+     * tooltip on the level select screen.
+     *
+     * @return {@code true} if the level is experimental
+     */
+    default boolean isLifecycleExperimental() {
+        // NOTE: Because CorruptedLevelSummary and SymlinkLevelSummary can have null settings, we need to check it
+        var settings = this.self().getSettings();
+
+        return settings != null && settings.getLifecycle().equals(com.mojang.serialization.Lifecycle.experimental());
+    }
+}