Four new examples, each of which is also the test surface for the thing it
demonstrates:
- datagrid — the DataGrid widget across five tabs (sheets with a formula
engine, big data, charts, pixels, widgets).
- portallist_hit — PortalList hit-testing, with a UI test suite.
- render_to_texture — the offscreen pass, with a UI test suite.
- splat_bench — Gaussian splat sorting and drawing under load.
uizoo gains a dropdown tab; the splash example's UI test follows the splash
host-services change.
