Code intel: fix merging of locations

Created by: chrismwendt

Previously, if an extension emitted from a references provider the locations [A, B] then [C], the references panel would show [C, B] because it did component-wise merging of the arrays. This blames to https://github.com/sourcegraph/sourcegraph/pull/2271/files#diff-a156849c8d06dcc9cd46e215d155d5bdR101

Now, the entire array is replaced when a references provider emits.

I ran into this while implementing fallback to basic-code-intel if the language server takes >Nms to return references.