[wasm] Implement System.Console.Clear (#43002)

* [wasm] Implement System.Console.Clear

* Add dummy console.clear implementation if it does not exist

* Initialize console in Clear

* Apply suggestions from codereview

src/libraries/System.Console/src/System.Console.csproj

@@ -236,4 +236,7 @@
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
     <Reference Include="System.Threading.Thread" />
   </ItemGroup>
+  <ItemGroup Condition=" '$(TargetsBrowser)' == 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Runtime.InteropServices.JavaScript\src\System.Private.Runtime.InteropServices.JavaScript.csproj" />
+  </ItemGroup>
 </Project>

src/libraries/System.Console/src/System/ConsolePal.WebAssembly.cs

@@ -6,6 +6,8 @@
 using System.Runtime.InteropServices;
 using Microsoft.Win32.SafeHandles;
 
+using JSObject = System.Runtime.InteropServices.JavaScript.JSObject;
+
 namespace System
 {
     internal sealed class WasmConsoleStream : ConsoleStream
@@ -74,6 +76,9 @@ public override void Flush()
 
     internal static class ConsolePal
     {
+        private static volatile bool s_consoleInitialized;
+        private static JSObject? s_console;
+
         private static Encoding? s_outputEncoding;
 
         internal static void EnsureConsoleInitialized() { }
@@ -163,7 +168,16 @@ public static string Title
             char sourceChar, ConsoleColor sourceForeColor,
             ConsoleColor sourceBackColor) => throw new PlatformNotSupportedException();
 
-        public static void Clear() => throw new PlatformNotSupportedException();
+        public static void Clear()
+        {
+            if (!s_consoleInitialized)
+            {
+                s_console = (JSObject)System.Runtime.InteropServices.JavaScript.Runtime.GetGlobalObject("console");
+                s_consoleInitialized = true;
+            }
+
+            s_console?.Invoke("clear");
+        }
 
         public static void SetCursorPosition(int left, int top) => throw new PlatformNotSupportedException();
 

src/mono/wasm/runtime-test.js

@@ -47,6 +47,7 @@ if (is_browser) {
 if (typeof console === "undefined") {
 	var Console = function () {
 		this.log = function(msg){ print(msg) };
+		this.clear = function() { };
 	};
 	console = new Console();
 }