[MSHARED-785] Make ConstantPoolParser ignore classes in unnamed package

[jhaber]

The ConstantPoolParser is looking for strings in the constant pool and treating them as references to a class which normally works fine, but it can create false-positives. The most common one we've run into is when there are classes in the unnamed package. For example, dnsjava has a class named update.java:
https://github.com/dnsjava/dnsjava/blob/0e56f37f320793ade4673cb2eaad159bc81d4a8a/update.java

So if you happen to have a string constant named "update", the dependency analyzer is fooled into thinking that this is a reference to update.java from dnsjava.

This PR mitigates the most common case by telling the ConstantPoolParser to ignore strings without a slash, as this should always correspond to a class in the unnamed package. This should never cause a false-negative, as according to the JLS:

types in an unnamed package cannot be imported

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[elharo]

This is a use case for Assume.

[jhaber]

👍 updated, let me know if you think I should make the same change to other tests in this class

[jhaber]

Gentle bump on this, let me know if there's anything I can do to help move this PR along

[slachiewicz]

merged, thx @jhaber

[jhaber]

🙇 thanks for integrating the change