runtime: move inconsistent memstats into gcController

runtime: move inconsistent memstats into gcController

Fundamentally, all of these memstats exist to serve the runtime in
managing memory. For the sake of simpler testing, couple these stats
more tightly with the GC.

This CL was mostly done automatically. The fields had to be moved
manually, but the references to the fields were updated via

    gofmt -w -r 'memstats.<field> -> gcController.<field>' *.go

For #48409.

Change-Id: Ic036e875c98138d9a11e1c35f8c61b784c376134
Reviewed-on: https://go-review.googlesource.com/c/go/+/397678
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>