Create a mouse-events feature

This is an old feature, but created to capture
`api.MouseEvent.movement{X,Y}` that, until this commit, were under the
`pointer-lock` feature. The properties work independently of pointer
lock, so it makes sense for them to live somewhere else.

This was prompted by mdn/content#34263.

features/mouse-events.yml

@@ -0,0 +1,39 @@
+name: Mouse events
+description: Mouse events, such as `click`, `mousedown`, or `mousemove`, fire when users interact with a pointing device such a mouse or trackpad.
+spec: https://w3c.github.io/uievents/#events-mouse-types
+compat_features:
+  # TODO: compute_from list
+  - api.Element.click_event
+  - api.Element.dblclick_event
+  - api.Element.mousedown_event
+  - api.Element.mouseup_event
+  - api.Element.mousemove_event
+  - api.Element.mouseout_event
+  - api.Element.mouseover_event
+  - api.MouseEvent
+  - api.MouseEvent.altKey
+  - api.MouseEvent.button
+  - api.MouseEvent.clientX
+  - api.MouseEvent.clientY
+  - api.MouseEvent.ctrlKey
+  - api.MouseEvent.metaKey
+  - api.MouseEvent.pageX
+  - api.MouseEvent.pageY
+  - api.MouseEvent.relatedTarget
+  - api.MouseEvent.screenX
+  - api.MouseEvent.screenY
+  - api.MouseEvent.shiftKey
+
+  # TODO: later additions
+  # - api.Element.mouseenter_event
+  # - api.Element.mouseleave_event
+  # - api.MouseEvent.MouseEvent
+  # - api.MouseEvent.buttons
+  # - api.MouseEvent.getModifierState
+  # - api.MouseEvent.offsetX
+  # - api.MouseEvent.offsetY
+  # - api.MouseEvent.x
+  # - api.MouseEvent.y
+  # Note that the next two were specified with `pointer-lock`, but work independently of it.
+  # - api.MouseEvent.movementX
+  # - api.MouseEvent.movementY

features/mouse-events.yml.dist

@@ -0,0 +1,15 @@
+# Generated from: mouse-events.yml
+# Do not edit this file by hand. Edit the source file instead!
+
+status:
+  baseline: high
+  baseline_low_date: 2015-07-29
+  baseline_high_date: 2018-01-29
+  support:
+    chrome: "2"
+    chrome_android: "18"
+    edge: "12"
+    firefox: "6"
+    firefox_android: "6"
+    safari: "4"
+    safari_ios: "3.2"

features/pointer-lock.yml

@@ -9,8 +9,6 @@ compat_features:
   - api.Document.pointerLockElement
   - api.Document.pointerlockerror_event
   - api.Element.requestPointerLock
-  - api.MouseEvent.movementX
-  - api.MouseEvent.movementY
   # Later additions:
   # - api.ShadowRoot.pointerLockElement
   # - html.elements.iframe.sandbox.allow-pointer-lock