Equip CIL with a mapping maintaining variable names before/after alpha conversion.

[michael-schwarz]

This is work by our student @faddeenkov which she undertook as part of her BA thesis.

The idea is to maintain a mapping between the original name a variable had in the C program and the name it has after the alpha-conversion performed by CIL.
This also adds a list of all CIL variables that are temporary variables created by CIL. Until now, there was no reliable way to see if a variable is a temporary CIL variable or not (at least as far as I am aware).

This seems relevant in quite a number of places:

• It is one of the prerequisites for merging the rest of the work for that thesis and Semantic Search analyzer#112 into Goblint (semantic search)
• It might be interesting to have this available for the HTML output
• This information might be helpful for generating witnesses (CC: @sim642)

[sim642]

Indeed, this would be good information to have for witness generation to make sure invariants only contain actual program variables and not CIL temporaries. Right now I have an ugly name-based heuristic for that:
https://github.com/goblint/analyzer/blob/a32a031712ca481fea1165e29f482ff782f40b27/src/domains/invariantCil.ml.

[michael-schwarz]

The CI status here on Github is not updated for some reason, both builds did in fact pass: https://travis-ci.com/github/goblint/cil/builds/190417919