Ability to discern between types directive and x-TypeScript-types

[dsherret]

For deno vendor, it might be nice to have a way to represent /// <reference types="..." /> and x-TypeScript-types separately in the graph while still providing a common method for the maybe_types_dependency.

This would also help us remove Range from being necessary for x-typescript-types as the types directive could have a range, but the x-typescript-types doesn't need one:

deno_graph/src/graph.rs

Lines 1331 to 1340 in f8adbe4

	if let Some(types_header) = headers.get("x-typescript-types") {
	let range = Range {
	specifier: module.specifier.clone(),
	start: Position::zeroed(),
	end: Position::zeroed(),
	};
	let resolved_dependency = resolve(types_header, &range, maybe_resolver);
	module.maybe_types_dependency =
	Some((types_header.clone(), resolved_dependency));
	}

Alternatively, I can just do a check for the start and end position all being zero, but that seems a little hacky.

[kitsonk]

I don't think they should specifically be seperate, as they represent the same functional concept, but should contain an optional range instead of a 0 range.

[dsherret]

Sure. I updated the title.