Update placeholder text with key bindings to focus context panel and navigate history (#19447)

Hopefully, this will help people understand how easy it is to add
context to an inline transformation.

![CleanShot 2024-10-18 at 22 41
00@2x](https://github.com/user-attachments/assets/c09c1d89-3df2-4079-9849-9de7ac63c003)

@as-cii @maxdeviant @rtfeldman could somebody update this to display the
actual correct key bindings and ship it. I have them hard coded for now.

Release Notes:

- Updated placeholder text with key bindings to focus context panel and
navigate history.

---------

Co-authored-by: Richard Feldman <oss@rtfeldman.com>

crates/assistant/src/prompts.rs

@@ -204,7 +204,7 @@ impl PromptBuilder {
         Ok(())
     }
 
-    pub fn generate_content_prompt(
+    pub fn generate_inline_transformation_prompt(
         &self,
         user_prompt: String,
         language_name: Option<&LanguageName>,