[FEATURE] Refactor SMT encoding option flag use

[rodrigo7491]

The new SMT encoding option flag is currently hardcoded in many places, making it hard to maintain it. We should have it as a global constant, as suggested by @Kukovec in #1093, and as an enum type instead of plain string, as suggested by @shonfeder in a discussion. A check for the correct encoding use by different symbolic state rewriter implementations also should be added, as suggested by @konnov in #1121.