Add auto-resizing to <perspective-viewer>

[texodus]

Adds auto-reiszing behavior (on by default) to <perspective-viewer>, via an internal ResizeHandler on these elements. As a result, notifyResize() is no longer needed for resizing strictly and will likely eventually be removed as it can lead to duplicate re-renders. For now, it has been preserved and behavior modified slightly - calling notifyResize() when auto-sizing is enabled will log a warning and disable auto-size, unless the force bool argument is provided.

Auto size behavior can be disabled, reverting to the old manual resize logic via notifyResize() (which will not warn in this case), by calling setAutoSize(false):

elem = document.querySelector("perspective-viewer");
elem.setAutoSize(false);
elem.notifyResize(); // No warning

[timkpaine]

I think the windows build got hung so i force cancelled it, but the webassembly build failed with:

Summary of all failing tests
 FAIL  packages/perspective-viewer-datagrid/test/js/superstore.spec.js (9.376s)
  ● superstore.html › pivot › by two rows and two columns

    expect(received).toBe(expected) // Object.is equality

    Expected: "cdaa134913bd6cae25d335ec477d5606"
    Received: "20da969a8500883c68e74abbc6de7ff3"