script: Pass more information to the MouseEvent constructor (#37672)

- Instead of eagerly computing `pageX` and `pageY`, collect the offset
  from the content's initial containing block in the compositor and pass
  that information through to `MouseEvent`. This prevents a layout flush
  that was happening when eagerly trying to fetch `Document` scroll
  offsets.
- Pass keyboard modifiers properly to `MouseEvent`.
- Now all this information is stored and passed as `Point2D` (typed) and
  `Modifiers` which greatly reduces the amount of arguments that need to
  be passed around.

Testing: It is difficult to test input events as they require WebDriver
which
isn't completely working yet. I have manually run Speedometer 2.1 and I
have
verified that this fixes the regression from #37601.
Fixes: #37601.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script_bindings/Cargo.toml

@@ -28,6 +28,7 @@ js = { workspace = true }
 jstraceable_derive = { path = "../jstraceable_derive" }
 libc = { workspace = true }
 log = { workspace = true }
+keyboard-types = { workspace = true }
 malloc_size_of = { workspace = true }
 malloc_size_of_derive = { workspace = true }
 num-traits = { workspace = true }

components/script_bindings/conversions.rs

@@ -22,9 +22,11 @@ use js::rust::{
     HandleId, HandleValue, MutableHandleValue, ToString, get_object_class, is_dom_class,
     is_dom_object, maybe_wrap_value,
 };
+use keyboard_types::Modifiers;
 use num_traits::Float;
 
 use crate::JSTraceable;
+use crate::codegen::GenericBindings::EventModifierInitBinding::EventModifierInit;
 use crate::inheritance::Castable;
 use crate::num::Finite;
 use crate::reflector::{DomObject, Reflector};
@@ -589,3 +591,52 @@ pub(crate) unsafe fn windowproxy_from_handlevalue<D: crate::DomTypes>(
     let ptr = value.to_private() as *const D::WindowProxy;
     Ok(DomRoot::from_ref(&*ptr))
 }
+
+impl<D: crate::DomTypes> EventModifierInit<D> {
+    pub fn modifiers(&self) -> Modifiers {
+        let mut modifiers = Modifiers::empty();
+        if self.altKey {
+            modifiers.insert(Modifiers::ALT);
+        }
+        if self.ctrlKey {
+            modifiers.insert(Modifiers::CONTROL);
+        }
+        if self.shiftKey {
+            modifiers.insert(Modifiers::SHIFT);
+        }
+        if self.metaKey {
+            modifiers.insert(Modifiers::META);
+        }
+        if self.keyModifierStateAltGraph {
+            modifiers.insert(Modifiers::ALT_GRAPH);
+        }
+        if self.keyModifierStateCapsLock {
+            modifiers.insert(Modifiers::CAPS_LOCK);
+        }
+        if self.keyModifierStateFn {
+            modifiers.insert(Modifiers::FN);
+        }
+        if self.keyModifierStateFnLock {
+            modifiers.insert(Modifiers::FN_LOCK);
+        }
+        if self.keyModifierStateHyper {
+            modifiers.insert(Modifiers::HYPER);
+        }
+        if self.keyModifierStateNumLock {
+            modifiers.insert(Modifiers::NUM_LOCK);
+        }
+        if self.keyModifierStateScrollLock {
+            modifiers.insert(Modifiers::SCROLL_LOCK);
+        }
+        if self.keyModifierStateSuper {
+            modifiers.insert(Modifiers::SUPER);
+        }
+        if self.keyModifierStateSymbol {
+            modifiers.insert(Modifiers::SYMBOL);
+        }
+        if self.keyModifierStateSymbolLock {
+            modifiers.insert(Modifiers::SYMBOL_LOCK);
+        }
+        modifiers
+    }
+}