checkers: add fixable for commentFormatting (#1190)

[okhowang]

Fixes #1190

[cristaloleg]

sgtm

[quasilyte]

This will add extra spaces inside comments:

//Comment with //inside other comment
=>
// Comment with // inside other comment

I don't think that it's a big deal, but it makes it less reliable in general as it does more changes than it should.

[okhowang]

This will add extra spaces inside comments:

//Comment with //inside other comment
=>
// Comment with // inside other comment

I don't think that it's a big deal, but it makes it less reliable in general as it does more changes than it should.

I use strings.Replace with n=1 which mean replace only first //

[quasilyte]

Ah, that's true.