Add a solver-independent SMT2 String parser/composer

[baierd]

We rely on specific SMT Solvers to parse and dump SMT2 formulas. Some solvers don't offer these API calls, while those that do print formulas arbitrarily for dump calls. Additionally, some solvers (e.g. Vampire) can only be used via SMT2 files.

Having a solver-independent String SMT2 parser that translates SMT2 files into their respective API calls for all supporting SMT solvers would allow us more freedom when choosing a solver.
Similarly, supporting solver-independent composing of SMT2 formulas allows us to easily share generated SMT2 files/Strings, even with solvers that don't offer an API.