Move vaadin-crud's default grid to light dom

[rolfsmeds]

Describe your motivation

The vaadin-crud web component's default grid is inside the CRUD's shadow DOM, making its parts inaccessible to the ::part() selector, unless we propagate all of them using exportparts. This is awkward due to the large number of parts, and would still not work with the proposed PartNameGenerator.

(This is not an issue for the Flow Crud component, nor for custom grids used with the Web Component, as in both cases the grid is in the Crud's light DOM.)

Describe the solution you'd like

Move vaadin-crud's default grid to light dom (which also makes it consistent with Flow and custom grid usage).

Describe alternatives you've considered

No response

Additional context

No response