ruff server: Ruff configuration from client settings overrides project configuration (#11062)

## Summary

This is a follow-up to https://github.com/astral-sh/ruff/pull/10984 that
implements configuration resolution for editor configuration. By 'editor
configuration', I'm referring to the client settings that correspond to
Ruff configuration/options, like `preview`, `select`, and so on. These
will be combined with 'project configuration' (configuration taken from
project files such as `pyproject.toml`) to generate the final linter and
formatter settings used by `RuffSettings`. Editor configuration takes
priority over project configuration.

In a follow-up pull request, I'll implement a new client setting that
allows project configuration to override editor configuration, as per
[this issue](https://github.com/astral-sh/ruff-vscode/issues/425).

## Review guide

The first commit, e38966d8843becc7234fa7d46009c16af4ba41e9, is just
doing re-arrangement so that we can pass the right things to
`RuffSettings::resolve`. The actual resolution logic is in the second
commit, 0eec9ee75c10e5ec423bd9f5ce1764f4d7a5ad86. It might help to look
at these comments individually since the diff is rather messy.

## Test Plan

For the settings to show up in VS Code, you'll need to checkout this
branch: https://github.com/astral-sh/ruff-vscode/pull/456.

To test that the resolution for a specific setting works as expected,
run through the following scenarios, setting it in project and editor
configuration as needed:

| Set in project configuration? | Set in editor configuration? |
Expected Outcome |

|-------------------------------|--------------------------------------------------|------------------------------------------------------------------------------------------|
| No | No | The editor should behave as if the setting was set to its
default value. |
| Yes | No | The editor should behave as if the setting was set to the
value in project configuration. |
| No | Yes | The editor should behave as if the setting was set to the
value in editor configuration. |
| Yes | Yes (but distinctive from project configuration) | The editor
should behave as if the setting was set to the value in editor
configuration. |

An exception to this is `extendSelect`, which does not have an analog in
TOML configuration. Instead, you should verify that `extendSelect`
amends the `select` setting. If `select` is set in both editor and
project configuration, `extendSelect` will only append to the `select`
value in editor configuration, so make sure to un-set it there if you're
testing `extendSelect` with `select` in project configuration.

crates/ruff_server/src/server/api/diagnostics.rs

@@ -6,7 +6,7 @@ pub(super) fn generate_diagnostics(snapshot: &DocumentSnapshot) -> Vec<lsp_types
     if snapshot.client_settings().lint() {
         crate::lint::check(
             snapshot.document(),
-            &snapshot.settings().linter,
+            snapshot.settings().linter(),
             snapshot.encoding(),
         )
     } else {