Fix audio engine init issue (#15922)

* Fix audio engine init issue

When the `Engine` constructor is called with a `WebGLRenderingContext` or `WebGL2RenderingContext`, the audio engine does not get initialized. This change fixes the issue by calling `Engine._sharedInit` with the WebGL rendering context's canvas.

Note that the WebGL rendering context's canvas may be an `OffscreenCanvas` and its type is cast to `HTMLCanvasElement` for the call to `Engine._sharedInit` because it would be a large change to make `AbstractEngine.__renderingCanvas` support both types. This is done the same way in the `WebGPUEngine` constructor, with the only consequence for the audio engine being that the mute button stays at the top-left of the document instead of automatically repositioning to the top-left of the canvas.

* Call `_sharedInit` from `ThinEngine` instead of `Engine`

packages/dev/core/src/Engines/engine.ts

@@ -375,12 +375,6 @@ export class Engine extends ThinEngine {
         this._features.supportRenderPasses = true;
 
         options = this._creationOptions;
-
-        if ((<any>canvasOrContext).getContext) {
-            const canvas = <HTMLCanvasElement>canvasOrContext;
-
-            this._sharedInit(canvas);
-        }
     }
 
     protected override _initGLContext(): void {

packages/dev/core/src/Engines/thinEngine.ts

@@ -283,7 +283,6 @@ export class ThinEngine extends AbstractEngine {
         let canvas: Nullable<HTMLCanvasElement> = null;
         if ((canvasOrContext as any).getContext) {
             canvas = <HTMLCanvasElement>canvasOrContext;
-            this._renderingCanvas = canvas;
 
             if (options.preserveDrawingBuffer === undefined) {
                 options.preserveDrawingBuffer = false;
@@ -398,7 +397,7 @@ export class ThinEngine extends AbstractEngine {
             }
         } else {
             this._gl = <WebGL2RenderingContext>canvasOrContext;
-            this._renderingCanvas = this._gl.canvas as HTMLCanvasElement;
+            canvas = this._gl.canvas as HTMLCanvasElement;
 
             if ((this._gl as any).renderbufferStorageMultisample) {
                 this._webGLVersion = 2.0;
@@ -413,6 +412,8 @@ export class ThinEngine extends AbstractEngine {
             }
         }
 
+        this._sharedInit(canvas);
+
         // Ensures a consistent color space unpacking of textures cross browser.
         this._gl.pixelStorei(this._gl.UNPACK_COLORSPACE_CONVERSION_WEBGL, this._gl.NONE);