runtime: move pacer time updates and state resets into methods
Currently GC pacer updates are applied somewhat haphazardly via direct
field access. To facilitate ease of testing, move these field updates
into methods. Further CLs will move more of these updates into methods.
For #44167.
Change-Id: I25b10d2219ae27b356b5f236d44827546c86578d
Reviewed-on: https://go-review.googlesource.com/c/go/+/309274
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com> Reviewed-by: Michael Pratt <mpratt@google.com>