Function with_layout_renderer 

pub fn with_layout_renderer<R>(
    text_scale: f32,
    f: impl FnOnce(&mut TextRenderer) -> R,
) -> R

Run f with a layout-only renderer at text_scale, for widgets that must measure in apply_layout, which is handed no renderer. Building one loads every installed font (tens of milliseconds) and layout runs every frame an animation is live, so renderers are pooled per thread; a nested call takes its own from the pool rather than borrowing the outer one.