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no longer represents the event itself, just the data needed to construct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/terminal_codegen.rs

@@ -6,7 +6,7 @@ use language_model::{
     ConfiguredModel, LanguageModelRegistry, LanguageModelRequest, report_assistant_event,
 };
 use std::{sync::Arc, time::Instant};
-use telemetry_events::{AssistantEvent, AssistantKind, AssistantPhase};
+use telemetry_events::{AssistantEventData, AssistantKind, AssistantPhase};
 use terminal::Terminal;
 
 pub struct TerminalCodegen {
@@ -79,7 +79,7 @@ impl TerminalCodegen {
 
                         let error_message = result.as_ref().err().map(|error| error.to_string());
                         report_assistant_event(
-                            AssistantEvent {
+                            AssistantEventData {
                                 conversation_id: None,
                                 kind: AssistantKind::InlineTerminal,
                                 message_id,