[css-cascade-6] Clarify circular dependency (In wording) in finding scoping limits. (#10295)

* [css-cascade-6] Clarify circular dependency in finding scoping limits.

Finding scoping limits mention in-scope elements, which in turn mentions scoping limits.

Add wording to ignore the scoping limits portion of in scope, which seems implied.

* Apply suggestion from @tabatkins

Inlining the relevant dfn instead, and making it non-inclusive.

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Co-authored-by: Tab Atkins Jr. <jackalmage@gmail.com>

Author: dshin-moz

css-cascade-6/Overview.bs

@@ -771,7 +771,8 @@ Identifying Scoping Roots and Limits</h4>
 	: Finding any [=scoping limits=]
 	:: For each [=scope=] created by a [=scoping root=],
 		its [=scoping limits=] are set to all elements
-		that are [=in scope=] and that match <<scope-end>>,
+		that are [=descendants=] of the [=scoping root=]
+		and that match <<scope-end>>,
 		interpreting '':scope'' and ''&''
 		exactly as in [=scoped style rules=].