feat(parser): recover missing tokens without consuming input

[jackprogramsjp]

Summary

• For the Expect function, append/insert a synthetic zero width token in the situation that the expected kind is missing, rather than just immediately advancing to the next real token
• Allow for incomplete editor-like input (e.g. missing ) / ] before the next let)
• Add parser tests which will cover on missing parenthesis recovery, EOF insertion, and missing bracket recovery

Test plan

• dotnet test all tests pass green