inline assistant: Use tools and remove insertion mode (#44248)

Co-authored by: Mikayla Maki <mikayla.c.maki@gmail.com>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

Release Notes:

- N/A

crates/feature_flags/src/flags.rs

@@ -11,3 +11,9 @@ pub struct PanicFeatureFlag;
 impl FeatureFlag for PanicFeatureFlag {
     const NAME: &'static str = "panic";
 }
+
+pub struct InlineAssistantV2FeatureFlag;
+
+impl FeatureFlag for InlineAssistantV2FeatureFlag {
+    const NAME: &'static str = "inline-assistant-v2";
+}