Unify WGSL AST node type introspection to use TypeCastTraits, replacing the ".isNodeKind()" call pattern with "is<NodeKind>(...)" to complement "downcast<NodeKind>(...)".
<rdar://problem/101943721>
Pull request: https://github.com/WebKit/WebKit/pull/6123
Committed 256381@main (480554208313): <https://commits.webkit.org/256381@main> Reviewed commits have been landed. Closing PR #6123 and removing active labels.