Auto merge of #135329 - oli-obk:push-sytltwnzxlrq, r=Noratrieb

Stable Hash: Ignore all HirIds that just identify the node itself

This should provide better incremental caching, but it seems there is more to it.

These IDs also serve no purpose being in the stable hash of the item they refer to, only when referring to *another* item is it important that we hash the `HirId`. So we can at least avoid the cost during stable hashing, even if we don't benefit from it by avoiding some queries' caches from being invalidated

Unsure how to make sure we do this right by construction. Would be nice to do something type based

Author: bors