editor: fix regression in editor extension "Search" functionality

Created by: slimsag

In https://github.com/sourcegraph/sourcegraph/pull/10586 I introduced a lot of tests for the editor API and also introduced a new "search in repo" API.

Unfortunately, this introduced a regression because my understanding of the API was wrong (so the test was testing the wrong thing), which caused all editor "Search" actions to perform a "Search in just this repo+file" instead of "Search globally" as users expect.

This adds a failing test for exactly the behavior editors rely on / that regression, and fixes that test + regression by changing the new "search in repo" API I introduced to use search_ prefixes.