runtime: convert g.atomicstatus to internal atomic type

runtime: convert g.atomicstatus to internal atomic type

Note that this changes some unsynchronized operations of g.atomicstatus to synchronized operations.

Updates #53821

Change-Id: If249d62420ea09fbec39b570942f96c63669c333
Reviewed-on: https://go-review.googlesource.com/c/go/+/425363
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>