ls: find references for attributes

[ankddev]

Hello! I imagine that finding references for attributes could be very useful. The most useful ones are finding references of deprecated, internal and external function/types. This could be useful e.g. when I'm reviewing what deprecated things to delete before breaking update, or when checking which things are not Gleam-native.

So, for externals it would look like this:

@external // <
pub type Wibble

@external(javascript, "./wibble_ffi.js", "wibble") // <
pub fn wibble() -> Wibble {
  todo
}

[lpil]

Could you expand a bit on the use cases please 🙏 I'm not sure when it would be used.