Expand Laurel implementation, so that tests T2 (impure expressions) and T3 (dag control flow) pass as well

[keyboardDrummer]

Changes

• Update testing infrastructure so the Laurel examples that include expected diagnostics can be run from the file where they are defined in.
  • Updated Laurel tests T1 to T10 to use this
• Add a ToFormat instance for the Laurel type to help with debugging
• Make changes so that Laurel test T2 and T3 pass.
  • This includes simple extensions to ConcreteToAbstractTreeTranslator and LaurelToBoogieTranslator, which perform 1-1 translations.
  • The most interesting change is the addition of LiftExpressionAssignments, which attempts to lift any assignments that occur in an expression position so they are done in the innermost enclosing statement block instead.

Caveats

I think there are a lot of cases of impure expressions that either don't translate correctly or fail to translate. It would be good to add explicit tests for those and to return not supported diagnostics in those cases. Created a GH issue to address something that's not supported: #282

Testing

• Laurel T2 and T3 are now running and passing as well.