Review Handler Collection logic around InvocationType

[joakime]

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Jetty version(s) 12.0.6

Jetty Environment Any

Java version/vendor (use: java -version) Any

OS type/version Any

Description While reviewing PR #11412 a question about the InvocationType logic in the various Handler Collection implementations was brought up.

See

• Handler.Sequence.setHandlers()
• PathMappingsHandler.addMapping()
• Handler.Singleton.updateHandler()
• HotSwapHandler.setHandler()
• WebSocketUpgradeHandler