gopls/v0.6.6

This release mostly included bug fixes and changes that are not user facing. A full list of all issues fixed can be found in the gopls/v0.6.6 milestone. To report a new problem, please file a new issue at https://golang.org/issues/new.

Thank you to our contributors!

@findleyr @heschik @pjweinb @muirdm @zchee @110y