Have read_file support images (#30435)

This is very basic support for them. There are a number of other TODOs
before this is really a first-class supported feature, so not adding any
release notes for it; for now, this PR just makes it so that if
read_file tries to read a PNG (which has come up in practice), it at
least correctly sends it to Anthropic instead of messing up.

This also lays the groundwork for future PRs for more first-class
support for images in tool calls across more image file formats and LLM
providers.

Release Notes:

- N/A

---------

Co-authored-by: Agus Zubiaga <hi@aguz.me>
Co-authored-by: Agus Zubiaga <agus@zed.dev>

crates/assistant_tools/src/web_search_tool.rs

@@ -3,7 +3,9 @@ use std::{sync::Arc, time::Duration};
 use crate::schema::json_schema_for;
 use crate::ui::ToolCallCardHeader;
 use anyhow::{Context as _, Result, anyhow};
-use assistant_tool::{ActionLog, Tool, ToolCard, ToolResult, ToolResultOutput, ToolUseStatus};
+use assistant_tool::{
+    ActionLog, Tool, ToolCard, ToolResult, ToolResultContent, ToolResultOutput, ToolUseStatus,
+};
 use futures::{Future, FutureExt, TryFutureExt};
 use gpui::{
     AnyWindowHandle, App, AppContext, Context, Entity, IntoElement, Task, WeakEntity, Window,
@@ -74,8 +76,10 @@ impl Tool for WebSearchTool {
             async move {
                 let response = search_task.await.map_err(|err| anyhow!(err))?;
                 Ok(ToolResultOutput {
-                    content: serde_json::to_string(&response)
-                        .context("Failed to serialize search results")?,
+                    content: ToolResultContent::Text(
+                        serde_json::to_string(&response)
+                            .context("Failed to serialize search results")?,
+                    ),
                     output: Some(serde_json::to_value(response)?),
                 })
             }