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_tool/src/assistant_tool.rs

@@ -19,6 +19,7 @@ use gpui::Window;
 use gpui::{App, Entity, SharedString, Task, WeakEntity};
 use icons::IconName;
 use language_model::LanguageModel;
+use language_model::LanguageModelImage;
 use language_model::LanguageModelRequest;
 use language_model::LanguageModelToolSchemaFormat;
 use project::Project;
@@ -65,21 +66,50 @@ impl ToolUseStatus {
 
 #[derive(Debug)]
 pub struct ToolResultOutput {
-    pub content: String,
+    pub content: ToolResultContent,
     pub output: Option<serde_json::Value>,
 }
 
+#[derive(Debug, PartialEq, Eq)]
+pub enum ToolResultContent {
+    Text(String),
+    Image(LanguageModelImage),
+}
+
+impl ToolResultContent {
+    pub fn len(&self) -> usize {
+        match self {
+            ToolResultContent::Text(str) => str.len(),
+            ToolResultContent::Image(image) => image.len(),
+        }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        match self {
+            ToolResultContent::Text(str) => str.is_empty(),
+            ToolResultContent::Image(image) => image.is_empty(),
+        }
+    }
+
+    pub fn as_str(&self) -> Option<&str> {
+        match self {
+            ToolResultContent::Text(str) => Some(str),
+            ToolResultContent::Image(_) => None,
+        }
+    }
+}
+
 impl From<String> for ToolResultOutput {
     fn from(value: String) -> Self {
         ToolResultOutput {
-            content: value,
+            content: ToolResultContent::Text(value),
             output: None,
         }
     }
 }
 
 impl Deref for ToolResultOutput {
-    type Target = String;
+    type Target = ToolResultContent;
 
     fn deref(&self) -> &Self::Target {
         &self.content