Filter unnecessary type suggestions in completion list

[mjbvz]

From microsoft/vscode#26340

Problem
When working in JavaScript files, we currently show the same suggestions as we do in TypeScript files. These suggestions include many interfaces and types that JavaScript users usually do not care about:

Proposed Fix
Suggestions for interfaces and types should only be returned in JavaScript contexts where they are actually useful, such as inside JSDoc

[mhegazy]

JSDoc should still be considered a type location.

We probably should also do a quick pass over gotodef and find all refs, to make sure we are filtering the results in the same way.

[mhegazy]

To clarify, this issue tracks filtering the entries in the completion list based on the location where the completion is requested. i.e. in a value postilion, type names are not returned, and in a type position, values names are not returned