Setup mac target for Fitness app

Improvements to demo game

They're just as crazy in this system as they are in the web.

```
enum DismissDirection {
  vertical,
  horizontal,
  left,
  right,
  up,
  down
}
```

To only enable dismissing to the right create the `Dismissable` with `direction: DismissDirection.right`. By default direction is `DismissDirection.horizontal` (left or right).

Updated the card_collection "Swipe Away" demo with a drawer that can be used to select one of the three X axis dismiss directions. Currently the MixedViewport class doesn't support horizontal scrolling, so the demo doesn't support the X axis dismiss directions.

Demo game improvements

Events should bubble up the tree

Error out on start if nothing started.

(optional param default value + newlines)

Previously we reversed the event path by mistake before dispatching events.

widget is actively ignoring or not by changing a boolean instead of
the tree structure. ignoring defaults to true.

defaultHitTestChildren should return whether it hit something

Some clients want to know whether they hit their children.

Fix minor problems in _ScrollGestureRecognizer, Dismissable, lerpColor

Alternating scroll gestures would sometimes be ignored because _ScrollGestureRecognizer didn't always reset its _state when the pointer[s] went up.

A Dismissable dismiss triggered by a drag and then a fling could cause the next attempt to drag-dismiss to fail.

Fixed the definition of lerpColor().

Alternating scroll gestures would sometimes be ignored because _ScrollGestureRecognizer didn't always reset its _state when the pointer[s] went up.

A Dismissable dismiss triggered by a drag and then a fling could cause the next attempt to drag-dimiss to fail.

Fixed the definition of lerpColor().

Adds power bar and movements to boss fights in demo game

These functions are now in sky:dart.

RenderFlex should handle overconstrainted constraints

Disable reparent during sync

This feature is causing a bug because the widget tree isn't correctly
synchronized with the render tree.

Rather than reading out the maxWidth, we should call constrainWidth to factor
in the minWidth, which might be bigger.

Change documentation for how to log using sky_tool

Actually make the raw examples work again

In my previous patch, I forgot to fill in the other diagonal entries in the
device transform matrix.

Remove all clients of sky.view.picture