Add refinements to the AI onboarding flow (#33738)

This includes making sure that both the agent panel and Zed's edit
prediction have a consistent narrative when it comes to onboarding users
into the AI features, considering the possible different plans and
conditions (such as being signed in/out, account age, etc.)

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <53836821+bennetbo@users.noreply.github.com>
Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>

crates/language_model/src/language_model.rs

@@ -654,7 +654,7 @@ pub enum LanguageModelProviderTosView {
     ThreadEmptyState,
     /// When there are no past interactions in the Agent Panel.
     ThreadFreshStart,
-    PromptEditorPopup,
+    TextThreadPopup,
     Configuration,
 }