Performance Optimisations on Project Setup

"Sorry I kinda put them into a single commit" - shedaniel

- Fix AtRemapper into not using ZipUtil#transformEntries, which is slow as it transverses the whole zip tree
- Optimises InnerClassRemapper into not using ZipUtil#iterate, which provides the InputStream of the ZipEntry, data that we don't utilize. Switch to a simple FileSystem to traverse through the list of files
- Make MappingsProvider respect mergedv2 yarn files, skipping merging and reordering namespaces in the process. Users that wish to benefit from this should switch to using mergedv2 yarn artifacts
- Make MinecraftMappedProvider only read inputs once
- Replace (TinyRemapper, official -> named) to (AsmRemapper, intermediary -> named), and chain it to the (TinyRemapper, official -> intermediary) to avoid reading the Minecraft jar again
- Multi-thread MinecraftPatchedProvider#fixParameterAnnotation properly

On a typical project, these changes can save up to 50% of the import time. Tested on architectury example mod, which brought import times from 1m 51s to 48s.

src/main/java/net/fabricmc/loom/util/ThreadingUtils.java

@@ -29,6 +29,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -121,4 +122,33 @@ public class ThreadingUtils {
 	public interface UnsafeConsumer<T> {
 		void accept(T value) throws Throwable;
 	}
+
+	public static TaskCompleter taskCompleter() {
+		return new TaskCompleter();
+	}
+
+	public static class TaskCompleter {
+		List<CompletableFuture<?>> tasks = new ArrayList<>();
+		ExecutorService service = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
+
+		public TaskCompleter add(UnsafeRunnable job) {
+			tasks.add(CompletableFuture.runAsync(() -> {
+				try {
+					job.run();
+				} catch (Throwable throwable) {
+					throw new RuntimeException(throwable);
+				}
+			}, service));
+			return this;
+		}
+
+		public void complete() {
+			try {
+				CompletableFuture.allOf(tasks.toArray(new CompletableFuture[0])).get();
+				service.shutdownNow();
+			} catch (InterruptedException | ExecutionException e) {
+				throw new RuntimeException(e);
+			}
+		}
+	}
 }