Merge #11347

Merge #11347

11347: fix: Fix resolution of eager macro contents r=jonas-schievink a=jonas-schievink

Eager macros resolve and expand any contained macro invocations before they are expanded. The logic for this was previously pretty broken: any nameres failure would be reported as a generic macro expansion error, so this didn't work correctly with the fixed-point resolution loop. This manifested as spurious errors whenever a non-legacy macro was used in an eager macro (that means *any* path with more than one segment).

After an intense staring contest with the abyss, this PR fixes the basic logic, but some bugs still remain (particularly around `$crate`). As a side-effect, this PR moves `ModPath` into `hir_expand`.

bors r+

Co-authored-by: Jonas Schievink <jonas.schievink@ferrous-systems.com>