Add TS Server API for mapping TS file to output file

## Search Terms - Debug / debugger - compile - tsserver ## Problem VS Code would like to make it easy to debug the active TS file just by pressing F5. To implement this, we need a way to map from a TypeScript file to its JavaScript output. See https://github.com/microsoft/vscode/issues/95544#issuecomment-628577083 for details ## Proposal Add a new TS Server API that takes a typescript file and returns the path to the output JavaScript file for it.