Reinstate limited symex renaming [blocks: #4164]

[tautschnig]

This is a clean revert of #3947, which in turn was a revert of the symex renaming improvements for TG's benefit. All changes in this PR have previously been approved, it is now up to TG maintainers to confirm that any issues have been fixed.

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• 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).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 39891fa).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/98742295

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 12c189a).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/100270085

[smowton]

@thk123 @allredj @tautschnig good news, I've got a test-gen bump (https://github.com/diffblue/test-gen/tree/smowton/wip/bump-disable-renaming-fix-object-factory) that brings this in, accompanied by some object factory type consistency improvements (CBMC working branch: https://github.com/smowton/cbmc/tree/smowton/wip/verify-members-and-limited-renaming-and-object-factory-fixes). I'm now trying to find a reasonable order to get the parts of that into cbmc.

[smowton]

@tautschnig now that #4161 is in, let's do this!

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 94dacc5).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/100611949