Waker::will_wake: Compare vtable address instead of its content

Optimize will_wake implementation by comparing vtable address instead
of its content.

The existing best practice to avoid false negatives from will_wake is
to define a waker vtable as a static item. That approach continues to
works with the new implementation.

While this potentially changes the observable behaviour, the function is
documented to work on a best-effort basis. The PartialEq impl for
RawWaker remains as it was.

Author: tmiasko

Diff for: library/core/src/task/wake.rs

@@ -313,7 +313,9 @@ impl Waker {
     #[must_use]
     #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn will_wake(&self, other: &Waker) -> bool {
-        self.waker == other.waker
+        let RawWaker { data: a_data, vtable: a_vtable } = self.waker;
+        let RawWaker { data: b_data, vtable: b_vtable } = other.waker;
+        a_data == b_data && ptr::eq(a_vtable, b_vtable)
     }
 
     /// Creates a new `Waker` from [`RawWaker`].