runtime: convert atomic values to runtime/internal/atomic types

[prattmic]

runtime/internal/atomic added Int32, etc types a while ago, which are slowing getting used on new code. We should also go through existing code and convert bare atomic values to use the atomic types.

[gopherbot]

Change https://go.dev/cl/417784 mentions this issue: runtime: convert gcController.dedicatedMarkWorkersNeeded to atomic type

[gopherbot]

Change https://go.dev/cl/417782 mentions this issue: runtime: convert gcController.fractionalMarkTime to atomic type

[gopherbot]

Change https://go.dev/cl/417775 mentions this issue: runtime: convert gcController.heapLive to atomic type

[gopherbot]

Change https://go.dev/cl/417778 mentions this issue: runtime: convert gcController.maxStackScan to atomic type

[gopherbot]

Change https://go.dev/cl/417783 mentions this issue: runtime: convert gcController.idleMarkTime to atomic type

[gopherbot]

Change https://go.dev/cl/417777 mentions this issue: runtime: convert gcController.lastStackScan to atomic type

[gopherbot]

Change https://go.dev/cl/417781 mentions this issue: runtime: convert gcController.dedicatedMarkTime to atomic type

[gopherbot]

Change https://go.dev/cl/417780 mentions this issue: runtime: convert gcController.bgScanCredit to atomic type

[gopherbot]

Change https://go.dev/cl/417776 mentions this issue: runtime: convert gcController.heapScan to atomic type

[gopherbot]

Change https://go.dev/cl/417779 mentions this issue: runtime: convert gcController.globalsScan to atomic type