Pull diagnostics fixes (#32242)

Follow-up of https://github.com/zed-industries/zed/pull/19230

* starts to send `result_id` in pull requests to allow servers to reply
with non-full results
* fixes a bug where disk-based diagnostics were offset after pulling the
diagnostics
* fixes a bug due to which pull diagnostics could not be disabled
* uses better names and comments for the workspace pull diagnostics part

Release Notes:

- N/A

crates/language/src/buffer.rs

@@ -127,6 +127,8 @@ pub struct Buffer {
     has_unsaved_edits: Cell<(clock::Global, bool)>,
     change_bits: Vec<rc::Weak<Cell<bool>>>,
     _subscriptions: Vec<gpui::Subscription>,
+    /// The result id received last time when pulling diagnostics for this buffer.
+    pull_diagnostics_result_id: Option<String>,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -955,6 +957,7 @@ impl Buffer {
             completion_triggers_timestamp: Default::default(),
             deferred_ops: OperationQueue::new(),
             has_conflict: false,
+            pull_diagnostics_result_id: None,
             change_bits: Default::default(),
             _subscriptions: Vec::new(),
         }
@@ -2740,6 +2743,14 @@ impl Buffer {
     pub fn preserve_preview(&self) -> bool {
         !self.has_edits_since(&self.preview_version)
     }
+
+    pub fn result_id(&self) -> Option<String> {
+        self.pull_diagnostics_result_id.clone()
+    }
+
+    pub fn set_result_id(&mut self, result_id: Option<String>) {
+        self.pull_diagnostics_result_id = result_id;
+    }
 }
 
 #[doc(hidden)]