R1:d1a1d4800143

Give ConduitAPIMethod->getMethodDescription() access to a real Viewer

Summary:
Ref T9964. The new `*.search` and `*.edit` methods generate documentation which depends on the viewer.

For example, the `*.search` methods show a reference table of the keys for all your saved queries.

Give them a real viewer to work with.

During normal execution, just populate this viewer with the request's viewer, so `$request->getViewer()` and `$this->getViewer()` both work and mean the same thing.

Test Plan: {F1023780}…