Rewrite download utils (#681)

- eTag support (It seems Mojang's CDN and our meta/maven do not support this right now)
- Age based caching.
- Sha1 based caching.
- HTTP(S) proxy settings should now be respected.
- The downloader has better awareness of offline mode and refresh deps, cleaning up the calling code a bit.
- Uses the new Java 11 HTTP client, provides async support for downloading multiple files
- Progress handling (TODO needs hooking up to gradle)
- Better compression support. Handled by [Methanol](https://mizosoft.github.io/methanol/) 
- Unit tested with a real web server.

src/main/java/net/fabricmc/loom/api/LoomGradleExtensionAPI.java

@@ -56,6 +56,7 @@ public interface LoomGradleExtensionAPI {
 
 	RegularFileProperty getAccessWidenerPath();
 
+	@Deprecated(forRemoval = true)
 	Property<Boolean> getShareRemapCaches();
 
 	default void shareCaches() {