Optimize (WasmRoot|WasmExternalRoot).clear (#77521)

Optimize (WasmRoot|WasmExternalRoot).clear to not use a memory barrier when zeroing a root for improved interop perf

src/mono/wasm/runtime/roots.ts

@@ -327,7 +327,10 @@ class WasmJsOwnedRoot<T extends MonoObject> implements WasmRoot<T> {
     }
 
     clear(): void {
-        this.set(<any>0);
+        // .set performs an expensive write barrier, and that is not necessary in most cases
+        //  for clear since clearing a root cannot cause new objects to survive a GC
+        const address32 = this.__buffer.get_address_32(this.__index);
+        Module.HEAPU32[address32] = 0;
     }
 
     release(): void {
@@ -420,7 +423,9 @@ class WasmExternalRoot<T extends MonoObject> implements WasmRoot<T> {
     }
 
     clear(): void {
-        this.set(<any>0);
+        // .set performs an expensive write barrier, and that is not necessary in most cases
+        //  for clear since clearing a root cannot cause new objects to survive a GC
+        Module.HEAPU32[<any>this.__external_address >>> 2] = 0;
     }
 
     release(): void {
@@ -432,4 +437,4 @@ class WasmExternalRoot<T extends MonoObject> implements WasmRoot<T> {
     toString(): string {
         return `[external root @${this.address}]`;
     }
-}
+}