[ty] Refactor "desperate" import resolution to use candidate operations that will also apply to module enumeration. (#28543)
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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
This is a small step towards the [larger
refactor](https://github.com/astral-sh/ruff/pull/28199) that will allow
us to share ordinary module resolution rules with the module enumeration
process required to [support namespace packages for auto
imports](https://github.com/astral-sh/ty/issues/2273) (please see that
refactor PR for a detailed description of our motivations). It refactors
the `desperately_resolve_name` method (used for ordinary module
resolution) to use methods of `NameResolver` that can be shared with
module enumeration.
## Test Plan
This is a pure refactor that relies on existing tests.
<!-- How was it tested? -->
ruff
d84df496 - [ty] Refactor "desperate" import resolution to use candidate operations that will also apply to module enumeration. (#28543)
