This PR implements #70601 as a private method, we wanted to do that as a private method and get it merged to facilitate testing on a broader scale while not committing to a particular API shape for everyone just yet. For scoping reasons, this is currently only tested for Windows x64, it should work on Windows x86 with a caveat that we will not establish a heap hard limit if we don't already have one. Any other platforms are not tested yet.

Before this change, we detect the physical memory (as well as the additional limits such as job objects) and configure the GC, and then we never change it. Some of these configurations are just some numeric fields on the gc_heap class, while some others are structural (e.g. number of heaps, region_range, etc ...).

This change aims at providing some flexibility on top of that init-once theme above. In particular, we allow the memory limit to change while the process is still running. It would be difficult to make structural changes, but it is relatively easy to just alter some numerical values. This change does just that. It factors out the memory-related settings into a separate function and allows them to be re-computed when the memory limit changes and the GC is notified through the RefreshMemoryLimit API call.

The technical challenge is commit accounting. If we happen to have no job object applied on the process and then one is applied later, now we have to set the heap_hard_limit, but then how would we know how much we already committed? The bulk of the refresh_memory_limit handles that by walking through the gc_heap data structure and figuring that out.

To make sure that is correct, a debug-only mode COMMITTED_BYTES_SHADOW is introduced. This mode will maintain the committed bytes all the time regardless of the existence of the heap_hard_limit, then we can assert the reconstructed value through the heap walking is producing the correct value as if we were tracking it all the time. This committed byte reconstruction and the testing knob will also be useful for other heap restructuring purposes.