script: Move WebGL DOM interfaces to script/dom/webgl/ (#38995)

Move interfaces defined by the WebGL spec to the `script/dom/webgl/
`module from `script/dom/`.

`script/dom/webgl*.rs` -> `script/dom/webgl/`
`script/dom/webgl_extensions` -> `script/dom/webgl/extensions`
`script/dom/webgl_validations` -> `script/dom/webgl/validations`

Testing: No changes, just a refactoring

Fixes (partially): #38901

Signed-off-by: Andrei Volykhin <volykhin.andrei@huawei.com>
Co-authored-by: Andrei Volykhin <volykhin.andrei@huawei.com>

components/script/dom/webgl/extensions/extension.rs

@@ -0,0 +1,43 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use canvas_traits::webgl::WebGLVersion;
+
+use super::WebGLExtensions;
+use crate::dom::bindings::reflector::DomObject;
+use crate::dom::bindings::root::DomRoot;
+use crate::dom::bindings::trace::JSTraceable;
+use crate::dom::webgl::webglrenderingcontext::WebGLRenderingContext;
+use crate::script_runtime::CanGc;
+
+/// Trait implemented by WebGL extensions.
+pub(crate) trait WebGLExtension: Sized
+where
+    Self::Extension: DomObject + JSTraceable,
+{
+    #[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
+    type Extension;
+
+    /// Creates the DOM object of the WebGL extension.
+    fn new(ctx: &WebGLRenderingContext, can_gc: CanGc) -> DomRoot<Self::Extension>;
+
+    /// Returns which WebGL spec is this extension written against.
+    fn spec() -> WebGLExtensionSpec;
+
+    /// Checks if the extension is supported.
+    fn is_supported(ext: &WebGLExtensions) -> bool;
+
+    /// Enable the extension.
+    fn enable(ext: &WebGLExtensions);
+
+    /// Name of the WebGL Extension.
+    fn name() -> &'static str;
+}
+
+pub(crate) enum WebGLExtensionSpec {
+    /// Extensions written against both WebGL and WebGL2 specs.
+    All,
+    /// Extensions writen against a specific WebGL version spec.
+    Specific(WebGLVersion),
+}