Fixes https://github.com/zed-industries/zed/issues/50218

- For every `Host` block: collect its host patterns (handling
continuations and filtering `!`/`*/\`), remember any `Hostname`.
- When the block ends: if `Hostname` is a git provider → discard
everything.
- Else if `Hostname` exists → keep all host aliases.
- Else → keep only the host aliases that are not git providers.

Added more extensive test coverage as well to cover the above!

Release Notes:

- Fixed SSH host picker showing git provider domains (e.g. github.com,
gitlab.com) from SSH config.

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Co-authored-by: Nathan Sobo <nathan@zed.dev>