Fix String initialiser type when java.lang.String is a stub

[owen-mc-diffblue]

Previously it was accidentally given type java.lang.Object, but we
didn't notice because we were less stringent about verifying type
equality (or, in transitioning from ID_symbol to ID_struct_tag for
Java types, we've become less generous about permitting a structural
match but name mismatch). Either way it was clearly wrong to assign
a wrong type like this.

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[smowton]

@owen-jones-diffblue please add a test for this -- janalyzer is actually a perfect vessel to test this as it can run the constant propagator, which checks for type consistency. I can reproduce the crash with janalyzer test.class --location-sensitive --constants --show, where test.class contains any string literal operations.

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 1365f8b).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/96094506

[owen-mc-diffblue]

I've added a test using janalyzer, and also a fix required to get janalyzer to run properly.

[tautschnig]

Please also add it to the Makefile.

[owen-mc-diffblue]

Oops. Well spotted.

[allredj]

🚫
This PR failed Diffblue compatibility checks (cbmc commit: 101e46e).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/96178128
Status will be re-evaluated on next push.
Please contact @peterschrammel, @thk123, or @allredj for support.

Common spurious failures:

• the cbmc commit has disappeared in the mean time (e.g. in a force-push)
• the author is not in the list of contributors (e.g. first-time contributors).

The incompatibility may have been introduced by an earlier PR. In that case merging this
PR should be avoided unless it fixes the current incompatibility.

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 0d96b0d).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/96192263