* Functions that take Stroke were updated to take Into<Stroke> to make
them consistent with other Into<Stroke> parameters.
* Vec2 implements DivAssign<f32>, to make it consistent with already
implementing MulAssign<f32> and Div<f32>.
* Vec2::angled() uses sin_cos() rather than an individual sin() and
cos() call for an immeasurable but hypothetical performance improvement.
* Disable the lock_reentry_single_thread() mutex test. Lock()ing twice
on the same thread is not guaranteed to panic.
* Closes <https://github.com/emilk/egui/issues/3419>.