Provide native touchpad scrolling on macOS

* etc/NEWS: Describe changes.
* lisp/term/ns-win.el (mouse-wheel-scroll-amount,
mouse-wheel-progressive-speed): Set to smarter values for macOS
touchpads.
* src/nsterm.m (emacsView::mouseDown): Use precise scrolling deltas to
calculate scrolling for touchpads and mouse wheels.
(syms_of_nsterm): Add variables 'ns-use-system-mwheel-acceleration',
'ns-touchpad-scroll-line-height' and 'ns-touchpad-use-momentum'.
* src/keyboard.c (make_lispy_event): Pass on .arg when relevant.
* src/termhooks.h (event_kind): Update comments re. WHEEL_EVENT.
* lisp/mwheel.el (mwheel-scroll): Use line count.
* lisp/subr.el (event-line-count): New function.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/termhooks.h b/src/termhooks.h
index 97c128ba4e2..b5171bf1229 100644
--- a/src/termhooks.h
+++ b/src/termhooks.h
@@ -116,7 +116,9 @@ enum event_kind
                                    .frame_or_window gives the frame
                                    the wheel event occurred in.
                                    .timestamp gives a timestamp (in
-                                   milliseconds) for the event.  */
+                                   milliseconds) for the event.
+                                   .arg may contain the number of
+                                   lines to scroll.  */
   HORIZ_WHEEL_EVENT,            /* A wheel event generated by a second
                                    horizontal wheel that is present on some
                                    mice. See WHEEL_EVENT.  */