Improve developer experience for parse tree extension updates

[pokey]

The problem

The extension sandbox can end up with an old version of an extension (especially the parse-tree extension), and it isn't clear that this has happened or what to do about it.

The solution

• Add --force argument to

  cursorless/src/test/initLaunchSandbox.ts

  Lines 24 to 31 in 660a961

  	const command = [
  	"code",
  	"--extensions-dir",
  	extensionSandboxDir,
  	...[...extensionDependencies, ...extraExtensions].flatMap(
  	(dependency) => ["--install-extension", dependency]
  	),
  	].join(" ");

  to force update on running yarn init-launch-sandbox
• Add file that tracks minimum version of parse-tree extension (just add field to package.json?)
• Check version of extension on extension load if we're in development mode, and if so fail, linking to instructions for update
• Add update instructions to documentation (yarn init-launch-sandbox)