TISTUD-6345 Use JSCA's "constants" values for function parameter Content Assist


- When we're inside arguments for a function invocation, or on a specific arg with a partial prefix, try to suggest possible "constants" defined for that argument in the function parameter model
- Introduce notion of IN_ARGUMENTS location type for JS (replacing the unused IN_PARAMETERS). This allows us to know when we're at a location where we should suggest arguments to a function invocation (which should suggest everything we would for IN_GLOBAL, but also more based on enumerated constants we get in JSCA).
- Update LocationTest to run much faster without having to index or any of that crap. As a result move it back into unit tests from integration suite