RFR: 8284942: Proxy building can just iterate superinterfaces once [v3]

[liach]

On Fri, 20 May 2022 00:08:36 GMT, Mandy Chung <mchung at openjdk.org> wrote:

> a named module can't have unnamed package

Since this is mandated by the Java Language Specification 7.4.2, I am tempted to change the thrown exception to `InternalError`, but I cannot find any restriction in the JVM Specification that prevents declaring a package-private superinterface in the unnamed package of a named module. If we can find a reference in the JVM Specification, I'm more than glad to refer to that in a comment and throw `InternalError` instead.

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PR: https://git.openjdk.java.net/jdk/pull/8281