go/analysis/passes/fieldalignment: add command

Add fieldalignment as a singlechecker.

Closes golang/go#43446

Change-Id: Ibc3bcc45087d56d429c66a74758b17bda01e7ef3
Reviewed-on: https://go-review.googlesource.com/c/tools/+/280617
Trust: Pontus Leitzler <leitzler@gmail.com>
Run-TryBot: Pontus Leitzler <leitzler@gmail.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

go/analysis/passes/fieldalignment/cmd/fieldalignment/main.go

@@ -0,0 +1,11 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+package main
+
+import (
+	"golang.org/x/tools/go/analysis/passes/fieldalignment"
+	"golang.org/x/tools/go/analysis/singlechecker"
+)
+
+func main() { singlechecker.Main(fieldalignment.Analyzer) }