0b9de40ced
DisplayList by default contains Skia paths stored as `SkPath` objects. Impeller must convert these to its internal `impeller::Path` format on every dispatch of the DisplayList on every frame. This change allows Impeller to store a cached copy of its version of the path into the DisplayList and reuse that instance if it ever encounters the same DisplayList again (likely to happen as most paths come from the Framework which does a lot of work to re-use ui.Picture objects - i.e. DisplayLists). In order to facilitate this change, `impeller::Path` was modified to have fast-copy-constructors that share the data and the PathBuilder will copy the mutable data into an immutable version in `TakePath()`.