Before
Private functions have RawVisibility module, but were
missed because take_types returned None early. After resolve_visibility
returned None, Visibility::Public was set instead and private functions
ended up being offered in autocompletion.

Choosing such a function results in an immediate error diagnostic
about using a private function.

After
Pattern match of take_types that returns None and
query for Module-level visibility from the original_module

Fix rust-lang#15134 - tested with a unit test and a manual end-to-end
test of building rust-analyzer from my branch and opening
the reproduction repository

REVIEW
Refactor to move scope_def_applicable and check function visibility
from a module

Please let me know what's the best way to add a unit tests to
nameres, which is where the root cause was

…ocomplete_2, r=Veykril

fix: Fix item tree lowering pub(self) to pub()

Prior to this, the item tree lowered `pub(self)` visibility to `pub()`
Fix rust-lang#15134 - tested with a unit test and
a manual end-to-end test of building rust-analyzer from my branch and opening the reproduction repository