Print a more helpful message in Java bytecode parsing invariant violation

[forejtv]

In Java bytecode parsing, we throw an invariant violation when we cannot find and opaque class for which we could infer a field referenced in another method X.m. To make debugging easier, we should be printing not only the field, its class, and referencing method m, but also the referencing class X.

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[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: aab30cb).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/112207762