Document how the binder and symbols work

[RyanCavanaugh]

Acknowledgement

• I acknowledge that issues using this template may be closed without further explanation at the maintainer's discretion.

Comment

"symbol" in this case refers to TypeScript's internal representation of declarations, not the JS Symbol() value.

Read the code and comments, experiment, etc, do whatever you have to, and write a technical overview of how symbols in TypeScript work. Someone reading this document should be able to explain the finer points of how resolveName works, and explain what happens in a code example like this

type x = number;
function fn(x: string) {
  let y: x = x;
}

Add your findings to .github/copilot-library.md. Aim for one to three written pages of content - enough to cover the important technical details, but not so much that it overwhelms your context window when you read it.