The documentation was converted from reStructuredText to Markdown, but a number of intra-tree links still pointed at .rst targets, so Sphinx could not resolve them. Point them at the .md files instead, covering both inline links and reference-style link definitions. Also fix three targets that were wrong beyond the extension: - the scalars page moved under telemetry/obsolete/ - the Browser Console anchor is browser-console-command-line - the Marionette index anchor is lowercase 'communication' This clears 98 'myst cross-reference target not found' warnings from ./mach doc (1003 -> 905). Differential Revision: https://phabricator.services.mozilla.com/D315853