[css-view-transitions-2] Exclude -ua-* and none in types (#14101)

* [css-view-transitions-2] Exclude `-ua-*` and `none` in types

Based on resolution #9534 (comment)
Closes #14081

* dash

* Make algorithm explicit

* Make more explicit

Author: noamr

css-view-transitions-2/Overview.bs

@@ -2033,6 +2033,15 @@ The [=@view-transition/types=] descriptor
 	The '<dfn for="@view-transition">types</dfn>' descriptor sets the [=ViewTransition/active types=] for the transition
 	when capturing or performing the transition, equivalent to calling {{Document/startViewTransition(callbackOptions)}} with that {{StartViewTransitionOptions/types}}.
 
+	<dl dfn-type=value dfn-for="@view-transition/types">
+		: <dfn>none</dfn>
+		:: No transition types are set.
+
+		: <dfn><<custom-ident>>+</dfn>
+		:: Sets the [=ViewTransition/active types=] for the transition to the specified custom identifiers.
+			 The <<custom-ident>> `none`, as well as any <<custom-ident>> starting with `-ua-`, are ignored.
+	</dl>
+
 	Note: the [=@view-transition/types=] descriptor only applies to the {{Document}} in which it is defined.
 	The author is responsible for using their chosen set of types in both documents.