Remove block_mouse_down in favor of stop_mouse_events_except_scroll (#30401)

This method was added in #20649 to be an alternative of `occlude` which
allows scroll events. It seems a bit arbitrary to only stop left mouse
downs, so this seems like it's probably an improvement.

Release Notes:

- N/A

crates/agent/src/inline_prompt_editor.rs

@@ -100,7 +100,7 @@ impl<T: 'static> Render for PromptEditor<T> {
         v_flex()
             .key_context("PromptEditor")
             .bg(cx.theme().colors().editor_background)
-            .block_mouse_down()
+            .block_mouse_except_scroll()
             .gap_0p5()
             .border_y_1()
             .border_color(cx.theme().status().info_border)