disallow render target resizing while in XR (#30738)

src/renderers/common/Renderer.js

@@ -1616,6 +1616,9 @@ class Renderer {
 	 */
 	setDrawingBufferSize( width, height, pixelRatio ) {
 
+		// Renderer can't be resized while presenting in XR.
+		if ( this.xr && this.xr.isPresenting ) return;
+
 		this._width = width;
 		this._height = height;
 
@@ -1639,6 +1642,9 @@ class Renderer {
 	 */
 	setSize( width, height, updateStyle = true ) {
 
+		// Renderer can't be resized while presenting in XR.
+		if ( this.xr && this.xr.isPresenting ) return;
+
 		this._width = width;
 		this._height = height;