Use Shopify/rbs's latest C parser implementation

[st0012]

Motivation

This PR adopts the latest RBS parser implementation from Shopify/rbs with a major refactor.

Some key changes:

1. Sorbet now needs to initialize a RBS global constant pool at the start of the process. Since Sorbet doesn't invoke its main in tests, we need to do it in its realmain module and the beginning of the testing pipeline
2. The new SignatureTranslator now performs both RBS parsing + translation in its translateType and translateSignature functions
   • With this, rbs::Type and rbs::MethodType structs become redundant as we don't need an intermediate data type
3. TypeTranslator and MethodTypeTranslator now store states like context and constant pool to reduce the number of parameters its functions need to keep passing down

Before

Unable to render rich display

Could not find a suitable point for the given distance

For more information, see https://docs.github.com/get-started/writing-on-github/working-with-advanced-formatting/creating-diagrams#creating-mermaid-diagrams

graph TD
    RBSSignaturesWalk -->|passes Comment| RBSParser
    RBSParser -->|returns MethodType or Type| RBSSignaturesWalk
    RBSParser -->|returns ParseError| RBSSignaturesWalk
    RBSSignaturesWalk -->|passes MethodType or Type| MethodTypeTranslator
    MethodTypeTranslator -->|uses Type| TypeTranslator

    subgraph Structs
        Comment
        ParseError
        MethodType
        Type
    end

    RBSSignaturesWalk --> Comment
    RBSParser --> Comment
    RBSParser --> ParseError
    RBSParser --> MethodType
    RBSParser --> Type
    MethodTypeTranslator --> MethodType
    MethodTypeTranslator --> Type
    TypeTranslator --> Type

After

Unable to render rich display

Could not find a suitable point for the given distance

For more information, see https://docs.github.com/get-started/writing-on-github/working-with-advanced-formatting/creating-diagrams#creating-mermaid-diagrams

graph TD
    RBSSignaturesWalk -->|creates| Comment
    RBSSignaturesWalk -->|passes Comment| SignatureTranslator
    SignatureTranslator -->|creates| Parser
    SignatureTranslator -->|uses| Comment
    SignatureTranslator -->|calls parseMethodType| Parser
    SignatureTranslator -->|calls parseType| Parser
    SignatureTranslator -->|passes Parser| MethodTypeTranslator
    MethodTypeTranslator -->|passes Parser| TypeTranslator

    subgraph Structs
        Comment
    end

    RBSSignaturesWalk --> Comment
    SignatureTranslator --> Comment

Test plan

See included automated tests.

[amomchilov]

That cleans up really nicely!

[amomchilov]

Nice.

[Morriar]

Overall looks good, I'm mostly concerned about the changes to realmain.cc