Fix non-thread-safe calls to Workspace.repository_locations and WorkspaceProcessContext.repository_locations
Summary: These are the last two lingering non-thread-safe methods on Workspace (I think). Using these methods runs the risk that a background thread will be messing with the list of repository_locations under the hood. Instead, require callers (almost none exist outside of tests - workspace telemetry appears to be the only 'real' one) to create a request context .
Test Plan: BK
Reviewers: sashank, alangenfeld, prha
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D8049