Add a lock file around building the loom cache. Regenerate if the lock file exists.

This helps to ensure that failed or canceled builds do not cause the cache to be left in an undetectable invalid state.

src/main/java/net/fabricmc/loom/LoomGradleExtension.java

@@ -109,4 +109,8 @@ public interface LoomGradleExtension extends LoomGradleExtensionAPI {
 	void addTransitiveAccessWideners(List<AccessWidenerFile> accessWidenerFiles);
 
 	DownloadBuilder download(String url);
+
+	boolean refreshDeps();
+
+	void setRefreshDeps(boolean refreshDeps);
 }