add go-consistent linter into CI

[quasilyte]

Run https://github.com/Quasilyte/go-consistent during CI checks.
Note that there are some warnings found by it right now:

astwalk/doc_comment_walker.go:3:1: unit import: omit parenthesis in a single-package import
astwalk/local_comment_walker.go:3:1: unit import: omit parenthesis in a single-package import
astwalk/local_def_visitor.go:3:1: unit import: omit parenthesis in a single-package import
astwalk/visitor.go:3:1: unit import: omit parenthesis in a single-package import
astwalk/walk_handler.go:3:1: unit import: omit parenthesis in a single-package import
linter/lintmain/lintmain.go:39:14: arg list parens: align `)` to a same line with last argument
linter/lintmain/lintmain.go:55:14: arg list parens: align `)` to a same line with last argument

They should be fixed along the way.

[peczenyj]

How can I help?