10738: internal: Do not search through all three namespaces in `ItemScope::name_of` r=Veykril a=Veykril
Brings down `5ms - find_path_prefixed (46 calls)` to `1ms - find_path_prefixed (46 calls)` for me on the `integrated_completion_benchmark`.
Still `O(n)` but this should considerably cut down lookups nevertheless(as shown by the timings already).
bors r+
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>
f724c84e7d