Chrome 147 enables concurrent and nested view transitions with element-scoped view transitions

Chrome 147 ships element-scoped view transitions, allowing developers to call `Element.startViewTransition()` on a DOM subtree rather than the entire document. This enables multiple view transitions to run concurrently, supports nesting of ongoing transitions, and fixes layering issues with `position: fixed` content while keeping the rest of the page interactive. Key behavioral defaults include self-participating scope roots, automatic containment of nested pseudo-elements, overflow clipping, and automatic application of `contain: layout` and `view-transition-scope: all` on the scope root during transitions. The feature graduated from developer testing in Chrome 140 to stable in Chrome 147 after collaboration with the CSS Working Group.