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/ai_onboarding/src/edit_prediction_onboarding_content.rs

@@ -0,0 +1,73 @@
+use std::sync::Arc;
+
+use client::{Client, UserStore};
+use gpui::{Entity, IntoElement, ParentElement};
+use ui::prelude::*;
+
+use crate::ZedAiOnboarding;
+
+pub struct EditPredictionOnboarding {
+    user_store: Entity<UserStore>,
+    client: Arc<Client>,
+    copilot_is_configured: bool,
+    continue_with_zed_ai: Arc<dyn Fn(&mut Window, &mut App)>,
+    continue_with_copilot: Arc<dyn Fn(&mut Window, &mut App)>,
+}
+
+impl EditPredictionOnboarding {
+    pub fn new(
+        user_store: Entity<UserStore>,
+        client: Arc<Client>,
+        copilot_is_configured: bool,
+        continue_with_zed_ai: Arc<dyn Fn(&mut Window, &mut App)>,
+        continue_with_copilot: Arc<dyn Fn(&mut Window, &mut App)>,
+        _cx: &mut Context<Self>,
+    ) -> Self {
+        Self {
+            user_store,
+            copilot_is_configured,
+            client,
+            continue_with_zed_ai,
+            continue_with_copilot,
+        }
+    }
+}
+
+impl Render for EditPredictionOnboarding {
+    fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let github_copilot = v_flex()
+            .gap_1()
+            .child(Label::new(if self.copilot_is_configured {
+                "Alternatively, you can continue to use GitHub Copilot as that's already set up."
+            } else {
+                "Alternatively, you can use GitHub Copilot as your edit prediction provider."
+            }))
+            .child(
+                Button::new(
+                    "configure-copilot",
+                    if self.copilot_is_configured {
+                        "Use Copilot"
+                    } else {
+                        "Configure Copilot"
+                    },
+                )
+                .full_width()
+                .style(ButtonStyle::Outlined)
+                .on_click({
+                    let callback = self.continue_with_copilot.clone();
+                    move |_, window, cx| callback(window, cx)
+                }),
+            );
+
+        v_flex()
+            .gap_2()
+            .child(ZedAiOnboarding::new(
+                self.client.clone(),
+                &self.user_store,
+                self.continue_with_zed_ai.clone(),
+                cx,
+            ))
+            .child(ui::Divider::horizontal())
+            .child(github_copilot)
+    }
+}