Support const args in type dependent paths (Take 2)

[lcnr]

once more, except it is sound this time 🥰 previously #71154

---

#![feature(const_generics)]

struct A;
impl A {
    fn foo<const N: usize>(&self) -> usize { N }
}
struct B;
impl B {
    fn foo<const N: usize>(&self) -> usize { 42 }
}

fn main() {
    let a = A;
    a.foo::<7>();
}

When calling type_of for generic const arguments, we now use the TypeckTables of the surrounding body to get the expected type.

This alone causes cycle errors though, as we now have typeck_tables_of(main) -> ... ->
type_of(main_ANON0 := 7) -> typeck_tables_of(main) ⚡ (see #68400 (comment))

To prevent this we must not call type_of(const_arg) during typeck_tables_of. This is achieved by
calling type_of(param_def_id) instead.

We have to somehow remember the DefId of the param through all of typeck, which is done using the
struct ty::WithOptConstParam<DefId>, which replaces DefId where needed and contains an Option<DefId> to
be able to store the const parameter in case it exists.

Queries which are currently cached on disk are split into two variants: query_name(cached) and query_name_(of|for)_const_arg(not cached), with query_name_of_const_arg taking a pair (did, param_did): (LocalDefId, DefId).

For some queries a method query_name_of_opt_const_arg is added to TyCtxt which takes a ty::WithOptConstParam and either calls query_name or query_name_of_const_arg depending on the value of const_param_did.

r? @eddyb @varkor

[rust-timer]

Queued e4220b3fb9c17c338cf69c14e8f91a7803b0d0b5 with parent 0c03aee, future comparison URL.

[rust-timer]

Finished benchmarking try commit (e4220b3fb9c17c338cf69c14e8f91a7803b0d0b5): comparison url.

[lcnr]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion

[bors]

⌛ Trying commit 26ad65e7ac660a24f37813cb754fcaa1db0d9940 with merge b68a4014ccd7f0a6a24bd4662f34b565ca658c28...

[lcnr]

@rust-timer build b68a4014ccd7f0a6a24bd4662f34b565ca658c28

[rust-timer]

Queued b68a4014ccd7f0a6a24bd4662f34b565ca658c28 with parent 70f9d23, future comparison URL.

[rust-timer]

Finished benchmarking try commit (b68a4014ccd7f0a6a24bd4662f34b565ca658c28): comparison url.

[lcnr]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion

[bors]

⌛ Trying commit 26f789f87b073a641d599e24c47d69d22b27c5a0 with merge 38457fb462ba475360cbcca5d21700c4e9b76596...

[bors]

☀️ Try build successful - checks-actions, checks-azure
Build commit: 38457fb462ba475360cbcca5d21700c4e9b76596 (38457fb462ba475360cbcca5d21700c4e9b76596)

[nnethercote]

This was a small perf loss, as expected.