java: do not use void reference

[kroening]

The concept of void * is borrowed from C. This commit changes void * to
a reference to java.lang.object.

The benefit is that we will be able to establish that all references in Java
are references to an object.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[smowton]

Before this works we might need to ensure that array types are based on Object

[thk123]

When I tried this before in #3992, it definitely broke things...

It broke because somehow a dynamically sized array got down to symex.

[thk123]

@smowton

that array types are based on Object

I'm not sure if this is what your question is referning to, but:

Object[] arr = new Object[4];
Object ao = arr;

Is valid Java

[smowton]

Sure, I meant that our representation should reflect that inheritance. Looks like we do though; once upon a time array[int] (for example) had a @class_identifier member; now it has a @java.lang.Object.

[TGWDB]

Closing this as it appears to be very old and failing (ancient) CI. Please reopen if you believe this is erroneous and will rebase/update.