fixed places related to heap hard limit configs

[Maoni0]

1. rename everywhere to heap hard limit instead of heap limit;
2. clarified when the GCHeapHardLimit and GCHeapHardLimitPercent configs are used;
3. switched the order of the link to GCHighMemPercent later to reflect its actual place in the doc (this also keeps the hard limit related configs together in the links section);

---

Internal previews

📄 File	🔗 Preview link
docs/core/runtime-config/garbage-collector.md	docs/core/runtime-config/garbage-collector
docs/standard/garbage-collection/fundamentals.md	docs/standard/garbage-collection/fundamentals

[gewarren]

Thank you.

Some bookmarks in other files will need to be updated too:

[Maoni0]

any more changes needed or could we merge this?