imagebitmap: Resolve promise with ImageBitmap on bitmap task source (#37488)

Follow the ImageBitmap specification and use the global scope bitmap
task source
to fulfill resolved promise (asynchronously). 
https://html.spec.whatwg.org/multipage/#bitmap-task-source

Any promise rejection must be done synchronously.

Testing: Improvements in the following WPT test
-
html/canvas/element/manual/imagebitmap/createImageBitmap-resolves-in-task.any.js

Fixes (partially): #34112

Signed-off-by: Andrei Volykhin <andrei.volykhin@gmail.com>

components/script/task_source.rs

@@ -22,6 +22,8 @@ use crate::task_manager::TaskManager;
 /// doesn't implement TaskSource.
 #[derive(Clone, Copy, Debug, Eq, Hash, JSTraceable, MallocSizeOf, PartialEq, VariantArray)]
 pub(crate) enum TaskSourceName {
+    /// <https://html.spec.whatwg.org/multipage/#bitmap-task-source>
+    Bitmap,
     Canvas,
     Clipboard,
     DOMManipulation,
@@ -48,6 +50,7 @@ pub(crate) enum TaskSourceName {
 impl From<TaskSourceName> for ScriptThreadEventCategory {
     fn from(value: TaskSourceName) -> Self {
         match value {
+            TaskSourceName::Bitmap => ScriptThreadEventCategory::ScriptEvent,
             TaskSourceName::Canvas => ScriptThreadEventCategory::ScriptEvent,
             TaskSourceName::Clipboard => ScriptThreadEventCategory::ScriptEvent,
             TaskSourceName::DOMManipulation => ScriptThreadEventCategory::ScriptEvent,