Major Performance Improvements (#548)

* Use WeakDom::into_raw for faster snapshot generation from models

* Make compute_patch_set take snapshots by value

* Stop deferring property application in apply_patch_set

* Use InstanceBuilder::empty to avoid extra name allocations

* Git dependencies, skip dropping ServeSession

* Use std::mem::forget instead of ManuallyDrop

* Switch to latest rbx-dom crates.io dependencies

* Update other dependencies

src/cli/build.rs

@@ -1,5 +1,6 @@
 use std::{
     io::{BufWriter, Write},
+    mem::forget,
     path::{Path, PathBuf},
 };
 
@@ -61,6 +62,10 @@ impl BuildCommand {
             }
         }
 
+        // Avoid dropping ServeSession: it's potentially VERY expensive to drop
+        // and we're about to exit anyways.
+        forget(session);
+
         Ok(())
     }
 }