telemetry_events: Rename AssistantEvent to AssistantEventData (#28133)

This PR renames the `AssistantEvent` type to `AssistantEventData`, as it
no longer represents the event itself, just the data needed to construct
it.

Pulling out of https://github.com/zed-industries/zed/pull/25179.

Release Notes:

- N/A

crates/agent/src/buffer_codegen.rs

@@ -28,7 +28,7 @@ use std::{
     time::Instant,
 };
 use streaming_diff::{CharOperation, LineDiff, LineOperation, StreamingDiff};
-use telemetry_events::{AssistantEvent, AssistantKind, AssistantPhase};
+use telemetry_events::{AssistantEventData, AssistantKind, AssistantPhase};
 
 pub struct BufferCodegen {
     alternatives: Vec<Entity<CodegenAlternative>>,
@@ -601,7 +601,7 @@ impl CodegenAlternative {
 
                         let error_message = result.as_ref().err().map(|error| error.to_string());
                         report_assistant_event(
-                            AssistantEvent {
+                            AssistantEventData {
                                 conversation_id: None,
                                 message_id,
                                 kind: AssistantKind::Inline,