For the gopls@v0.12.0 release, we want to make it easy for users to collect relevant information about the size (and shape) of their workspace, so that we can use this when collecting feedback about performance of the prerelease / release.

A new subcommand seems like the easiest way to do this. We should probably give this command a generic name (such as stats) so that we can extend it in the future with any additional diagnostic information.