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/find_path_tool.rs

@@ -1,6 +1,8 @@
 use crate::{schema::json_schema_for, ui::ToolCallCardHeader};
 use anyhow::{Result, anyhow};
-use assistant_tool::{ActionLog, Tool, ToolCard, ToolResult, ToolResultOutput, ToolUseStatus};
+use assistant_tool::{
+    ActionLog, Tool, ToolCard, ToolResult, ToolResultContent, ToolResultOutput, ToolUseStatus,
+};
 use editor::Editor;
 use futures::channel::oneshot::{self, Receiver};
 use gpui::{
@@ -126,7 +128,7 @@ impl Tool for FindPathTool {
                     write!(&mut message, "\n{}", mat.display()).unwrap();
                 }
                 Ok(ToolResultOutput {
-                    content: message,
+                    content: ToolResultContent::Text(message),
                     output: Some(serde_json::to_value(output)?),
                 })
             }