tidy: condense variable declarations

Created by: rvantonder

Condenses consecutive variable declarations with the same type. Example:

var x int
var y int

becomes

var x, y int

Created with

{
    "matchTemplate": "var :[[x]] :[t.] var :[[y]] :[t.]",
    "rewriteTemplate": "var :[[x]], :[[y]] :[[t]]",
    "scopeQuery": "repo:github.com/sourcegraph/sourcegraph$ lang:go"
}