track whether a non-coherence `TypingMode` has been used to reuse cache entries

[lcnr]

see the WIP branch https://github.com/lcnr/rust/tree/typing-mode-is-coherence.

It is now fairly straightforward to track whether evaluation relied on the exact typing mode. finishing this work should result in a reasonable perf improvement

[lcnr]

See the perf results in #133242 (comment) which accidentally stopped tracking the TypingMode entirely for a rough estimate of the potential impact