PSA: CSS view transitions: match-element is temporarily disallowed as a view-transition-name

[Noam Rosenthal]

In preparation of supporting { view-transition-name: match-element } as a value that generates automatic view transition names for elements based on their identity, the next Chrome release (M133) disables that value as a valid custom ident for view-transition-name.

When view-transition-name: match-element ships, this name would have the specified behavior.

We're disabling it temporarily to prevent future backwards compatibility issues when this is shipped.

This change would only affect pages that explicitly use or intend to use the name "match-element" for a particular view-transition-name, which should be a very rare occurrence if it exists at all.