Update Z3 to Version 4.15.2

[baierd]

Z3 had several updates since we updated to 4.14.0 and is currently at 4.15.2.
We should update our version accordingly.

There are not that many changes besides improvements and bug fixes, so this should go smoothly.

[kfriedberger]

Step 1: publish Z3 to Ivy. This was recently done for versions 4.13.4, 4.14.1, 4.15.0, 4.15.1, 4.15.2 ✔️

Step 2: stage Z3 to Maven. This is broken, see #385. This step can also be done later. ❌

Step 3: test JavaSMT with each version, at least basic tests like Unit tests in CI. This is done with a new branch https://github.com/sosy-lab/java-smt/commits/z3/version-update-from-4.14.0/ ✔️

Step 4: merge into master, see PR #497 ✔️