LSIF support for FSAC

The Language Server Index Format (LSIF, pronounced “else if”) is a standard format for [language servers](https://langserver.org/) or other programming tools to emit their knowledge about a code workspace. This persisted information can later be used to answer LSP requests for the same workspace without running a language server. More info about can be found [on the official website](https://lsif.dev/).

As per Twitter thread (https://twitter.com/k_cieslak/status/1500910214039678978), wanted to create a tracking issue for LSIF support in FSAC I am currently working on.