Support prioritizing discovered TOML settings over editor settings

[snowsignal]

Summary

Fixes https://github.com/astral-sh/ruff-vscode/issues/425 (though only in the pre-release version, since this is a feature for the new LSP server)

This is a follow-up to https://github.com/astral-sh/ruff-vscode/pull/456.

A new setting has been introduced, Prioritize File Configuration, which tells the extension to prioritize settings from discovered TOML files over extension settings. Extension settings will still be used when a set field in the extension is not set in the file configuration.

Test Plan

Refer to https://github.com/astral-sh/ruff/pull/11086 for a test plan.