The WrongOneOf check also fails with the new arrow-type switch expressions #2393

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Description of the problem / feature request:

The WrongOneOf check also fails with the new arrow-type switch expressions.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

switch (proto.oneOfCase()) {
  case BLAH -> {...};
  default -> {...};
}

What version of Error Prone are you using?

2.6.0

Have you found anything relevant by searching the web?

Same fix required as #2371 and #2124 here