It was originally designed for faster trasmission of syntax trees from
C++ to SwiftSyntax, but superceded by the CLibParseActions. There's no
deserializer for it anymore, so let's just remove it.
Enhances `swift-syntax-test` to output the parser diagnostics so we can verify that
if the incremental parse resulted in parser diagnostics, those diagnostics were also emitted during the full parse.
Add a shared library with a C API that provides access to the syntactic parser with callbacks for the inference of raw syntax nodes.
This is primarily intended to be used by SwiftSyntax to speed-up source code parsing for it.
