Relands https://github.com/zed-industries/zed/pull/36441 with a
deserialization fix.

Previously, deserializing `"includeText"` into
`lsp::TextDocumentSyncSaveOptions` resulted in a `Supported(false)` type
instead of `SaveOptions(SaveOptions { include_text: Option<bool> })`.

```rs
impl From<bool> for TextDocumentSyncSaveOptions {
    fn from(from: bool) -> Self {
        Self::Supported(from)
    }
}
```

Looks like, while dynamic registartion we only get `SaveOptions` type
and never `Supported` type.
(https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocumentSaveRegistrationOptions)

Release Notes:

- N/A

---------

Co-authored-by: Lukas Wirth <lukas@zed.dev>