Allow LSP adapters to decide, which diagnostics to underline (#31450)

Closes
https://github.com/zed-industries/zed/pull/31355#issuecomment-2910439798

<img width="1728" alt="image"
src="https://github.com/user-attachments/assets/2eaa8e9b-00bc-4e99-ac09-fceb2d932e41"
/>


Release Notes:

- N/A

crates/language/src/proto.rs

@@ -213,6 +213,7 @@ pub fn serialize_diagnostics<'a>(
             } as i32,
             group_id: entry.diagnostic.group_id as u64,
             is_primary: entry.diagnostic.is_primary,
+            underline: entry.diagnostic.underline,
             code: entry.diagnostic.code.as_ref().map(|s| s.to_string()),
             code_description: entry
                 .diagnostic
@@ -429,6 +430,7 @@ pub fn deserialize_diagnostics(
                     is_primary: diagnostic.is_primary,
                     is_disk_based: diagnostic.is_disk_based,
                     is_unnecessary: diagnostic.is_unnecessary,
+                    underline: diagnostic.underline,
                     data,
                 },
             })