Rewrite/solc parsing

[0xalpharush]

This PR updates @samczsun's work on #627 to be compatible with addition of SlitherCompilationUnit and the addition of things like user defined value types and unchecked blocks. This greatly improves the typing of the code

I think the failing tests might just need to be updated rather than conformed to:

• the test conditional-all is failing parser tests bc the node id changes but the CFG is the same
• some of the reentrancy tests fail bc the existing implementation doesn't create a tuple with None for (success,) = call()

TODO:

• fix linting
• add types for symbol alias and using for parsing and move out of compilation unit