fix: import trait associated items for builtin types

[KrishnaAdityaSrivastava]

Summary

Fixes #23135.

Trait associated items can be accessed through builtin types, but rust-analyzer previously failed to offer the corresponding import/completion for paths such as:

fn main() {
    bool::fmt(todo!());
}

rustc resolves fmt through traits such as core::fmt::Debug and core::fmt::Display, but rust-analyzer did not find those trait candidates during qualified-path import resolution.

Changes

• Handle builtin types when resolving qualified-path imports.
• Consider applicable trait candidates when resolving associated items on the resolved type.
• Generate the appropriate trait import when the associated item comes from a trait.
• Preserve the existing import resolution path for modules and other qualifiers.
• Add a regression test for trait associated items accessed through bool.

Tests

• cargo test -p ide-completion flyimport
• cargo clippy -p ide-db -p ide-completion --all-targets -- --cap-lints warn
• cargo xtask tidy

[ChayimFriedman2]

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