Insert and Add menus scroll on large Windows displays

On Windows, Studio's Insert menu and matching toolbar Add flyout could become scrollable on large displays even when there was enough room to show the full menu. The menu commands were still present, but some were hidden behind scroll buttons because the Semi.Avalonia menu flyout height budget was too small for Studio's longest menus.

Expected behaviour: Studio should show the full Insert/Add menu on normal desktop displays and reserve menu scrolling for compact displays where the popup genuinely cannot fit.

Fixed in ce51c0da by overriding the Semi menu flyout height token in Studio's theme overrides and adding a regression test that checks the current Insert menu fits the configured budget.