script: Move canvas stuff into dom/canvas folder (#39071)

Move all canvas stuff to canvas folder and 2d canvas to canvas/2d
folder. Webgl and webgpu context remain in respective folders as
outlined in
https://github.com/servo/servo/issues/38901#issuecomment-3243020235

Testing: Just refactor.
Part of https://github.com/servo/servo/issues/38901

---------

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

components/script/dom/canvas/2d/canvasgradient.rs

@@ -0,0 +1,108 @@
+/* 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::canvas::{
+    CanvasGradientStop, FillOrStrokeStyle, LinearGradientStyle, RadialGradientStyle,
+};
+use dom_struct::dom_struct;
+
+use super::canvas_state::parse_color;
+use crate::dom::bindings::cell::DomRefCell;
+use crate::dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasGradientMethods;
+use crate::dom::bindings::error::{Error, ErrorResult};
+use crate::dom::bindings::num::Finite;
+use crate::dom::bindings::reflector::{Reflector, reflect_dom_object};
+use crate::dom::bindings::root::DomRoot;
+use crate::dom::bindings::str::DOMString;
+use crate::dom::globalscope::GlobalScope;
+use crate::script_runtime::CanGc;
+
+// https://html.spec.whatwg.org/multipage/#canvasgradient
+#[dom_struct]
+pub(crate) struct CanvasGradient {
+    reflector_: Reflector,
+    style: CanvasGradientStyle,
+    #[no_trace]
+    stops: DomRefCell<Vec<CanvasGradientStop>>,
+}
+
+#[derive(Clone, JSTraceable, MallocSizeOf)]
+pub(crate) enum CanvasGradientStyle {
+    Linear(#[no_trace] LinearGradientStyle),
+    Radial(#[no_trace] RadialGradientStyle),
+}
+
+impl CanvasGradient {
+    fn new_inherited(style: CanvasGradientStyle) -> CanvasGradient {
+        CanvasGradient {
+            reflector_: Reflector::new(),
+            style,
+            stops: DomRefCell::new(Vec::new()),
+        }
+    }
+
+    pub(crate) fn new(
+        global: &GlobalScope,
+        style: CanvasGradientStyle,
+        can_gc: CanGc,
+    ) -> DomRoot<CanvasGradient> {
+        reflect_dom_object(
+            Box::new(CanvasGradient::new_inherited(style)),
+            global,
+            can_gc,
+        )
+    }
+}
+
+impl CanvasGradientMethods<crate::DomTypeHolder> for CanvasGradient {
+    // https://html.spec.whatwg.org/multipage/#dom-canvasgradient-addcolorstop
+    fn AddColorStop(&self, offset: Finite<f64>, color: DOMString) -> ErrorResult {
+        if *offset < 0f64 || *offset > 1f64 {
+            return Err(Error::IndexSize);
+        }
+
+        let color = match parse_color(None, &color) {
+            Ok(color) => color,
+            Err(_) => return Err(Error::Syntax(None)),
+        };
+
+        self.stops.borrow_mut().push(CanvasGradientStop {
+            offset: (*offset),
+            color,
+        });
+        Ok(())
+    }
+}
+
+pub(crate) trait ToFillOrStrokeStyle {
+    fn to_fill_or_stroke_style(self) -> FillOrStrokeStyle;
+}
+
+impl ToFillOrStrokeStyle for &CanvasGradient {
+    fn to_fill_or_stroke_style(self) -> FillOrStrokeStyle {
+        let gradient_stops = self.stops.borrow().clone();
+        match self.style {
+            CanvasGradientStyle::Linear(ref gradient) => {
+                FillOrStrokeStyle::LinearGradient(LinearGradientStyle::new(
+                    gradient.x0,
+                    gradient.y0,
+                    gradient.x1,
+                    gradient.y1,
+                    gradient_stops,
+                ))
+            },
+            CanvasGradientStyle::Radial(ref gradient) => {
+                FillOrStrokeStyle::RadialGradient(RadialGradientStyle::new(
+                    gradient.x0,
+                    gradient.y0,
+                    gradient.r0,
+                    gradient.x1,
+                    gradient.y1,
+                    gradient.r1,
+                    gradient_stops,
+                ))
+            },
+        }
+    }
+}