tauri-runtime-servocat 3.20.0

Servo-replacement runtime for Tauri: wires html-cat, css-cat, dom-cat, layout-cat, paint-cat, net-cat, boa-cat, ecma-runtime-cat, and web-api-cat into a single rendering + scripting pipeline. v3.20.0 picks up web-api-cat 0.7.5: user-supplied webview scripts can now call `event.preventDefault()` / `stopPropagation()` / `stopImmediatePropagation()` on the event Object that `dispatchEvent` passes to listeners, plus read the canonical Event spec slots `target` / `currentTarget` / `defaultPrevented`. No tauri-runtime-servocat source change beyond the manifest -- the dep bump exposes the new surface to scripts uniformly. Seventh sub-crate of a Servo-replacement webview runtime targeting Tauri.