internal: even more `tracing`
As part of profiling completions, I added some additional spans and moved `TyBuilder::subst_for_def` closer to its usage site (the latter had a small impact on completion performance. Thanks for the tip, Lukas!)
rust-analyzer has logic that discounts suggesting `use`s for private
imports, but that logic is unnecessarily strict - for instance given
this code:
```rust
mod foo {
pub struct Foo;
}
pub(crate) use self::foo::*;
mod bar {
fn main() {
Foo$0;
}
}
```
... RA will suggest to add `use crate::foo::Foo;`, which not only makes
the code overly verbose (especially in larger code bases), but also is
disjoint with what rustc itself suggests.
This commit adjusts the logic, so that `pub(crate)` imports are taken
into account when generating the suggestions; considering rustc's
behavior, I think this change doesn't warrant any extra configuration
flag.
Note that this is my first commit to RA, so I guess the approach taken
here might be suboptimal - certainly feels somewhat hacky, maybe there's
some better way of finding out the optimal import path 😅
