Allow to feed a value in another query's cache and remove `WithOptConstParam` by...

I used it to remove WithOptConstParam queries, as an example.

The idea is that a query (here typeck(function)) can write into another query's cache (here type_of(anon const)). The dependency node for type_of would depend on all the current dependencies of typeck.

There is still an issue with cycles: if type_of(anon const) is accessed before typeck(function), we will still have the usual cycle. The way around this issue is to ensure that typeck(function) is called before accessing type_of(anon const).

When replayed, we may the following cases:

• typeck is green, in that case type_of is green too, and all is right;
• type_of is green, typeck may still be marked as red (it depends on strictly more things than type_of) -> we verify that the saved value and the re-computed value of type_of have the same hash;
• type_of is red, then typeck is red -> it's the caller responsibility to ensure typeck is recomputed before type_of.

As anon consts have their own DefPathData, it's not possible to have the def-id of the anon-const point to something outside the original function, but the general case may have to be resolved before using this device more broadly.

There is an open question about loading from the on-disk cache. If typeck is loaded from the on-disk cache, the side-effect does not happen. The regular type_of implementation can go and fetch the correct value from the decoded typeck results, and the dep-graph will check that the hashes match, but I'm not sure we want to rely on this behaviour.

I specifically allowed to feed the value to type_of from inside a call to type_of. In that case, the dep-graph will check that the fingerprints of both values match.

This implementation is still very sensitive to cycles, and requires that we call typeck(function) before typeck(anon const). The reason is that typeck(anon const) calls type_of(anon const), which calls typeck(function), which feeds type_of(anon const), and needs to build the MIR so needs typeck(anon const). The latter call would not cycle, since type_of(anon const) has been set, but I'd rather not remove the cycle check.