Add `isVideoFrameTexture=true` in VideoFrameTexture (#30381)

* brand

* doc

* ci

* Update VideoFrameTexture.js

* html doc, not jsdoc

---------

Co-authored-by: Michael Herzog <michael.herzog@human-interactive.org>

docs/api/en/textures/VideoFrameTexture.html

@@ -79,6 +79,9 @@
 
 		<p>See the base [page:VideoTexture VideoTexture] class for common properties.</p>
 
+		<h3>[property:Boolean isVideoFrameTexture]</h3>
+		<p>Read-only flag to check if a given object is of type [name].</p>
+
 		<h2>Methods</h2>
 
 		<p>See the base [page:VideoTexture VideoTexture] class for common methods.</p>

src/textures/VideoFrameTexture.js

@@ -6,6 +6,8 @@ class VideoFrameTexture extends VideoTexture {
 
 		super( {}, mapping, wrapS, wrapT, magFilter, minFilter, format, type, anisotropy );
 
+		this.isVideoFrameTexture = true;
+
 	}
 
 	update() {