Add active_cursor_position to CodeEditorView for IME positioning (warpdotdev#9555)

## Description
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it contains any UI changes! -->
- Fixes IME candidate window positioning for the code editor on macOS.
- `CodeEditorView` now provides `active_cursor_position()` so the IME
anchor can be derived from the code editor caret instead of falling back
to stale positions from other inputs (e.g. terminal input).
- Uses current-frame caret geometry with a last-frame fallback to keep
placement stable during fast composition/layout timing.

## Testing
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- Manual (macOS):
  - Opened a workspace with both a terminal pane and a code editor pane.
- Typed with Chinese IME in terminal first (candidate popup follows
terminal caret).
- Switched to code editor and typed with IME; verified candidate popup
now anchors near the code editor caret instead of staying at terminal
coordinates.
- Repeated with mouse selection/caret moves in the code editor; verified
IME popup remains correctly anchored in editor context.
- Automated:
  - Ran `cargo check -p warpui --lib` locally after changes.

No new automated tests were added because this bug is tied to macOS IME
runtime behavior and AppKit caret query timing
(`firstRectForCharacterRange`) that is difficult to reliably simulate in
existing unit/integration test harnesses.

## Server API dependencies
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dependencies. -->
- [ ] Is this change necessary to make the client compatible with a
desired [server API breaking
change](https://www.notion.so/warpdev/How-to-safely-introduce-server-API-breaking-changes-0aa805ff5d5d41fd8834f3c95caba0b4?pvs=4#d55ecf8aea3449949d3c33b0e67f6800)?
- [ ] Does this change rely on a [new server
API](https://www.notion.so/warpdev/How-to-add-a-new-full-stack-feature-8412cede405a4ec194b32bdd4b951035?pvs=4#04da1e6a493542d68b3e998c7d339640)?
- [ ] If so, is the use of this API restricted to client channels that
rely on the staging server (e.g. WarpDev)?
- [ ] Is this change enabling the use of a server API on client channels
that rely on the production server (e.g. WarpStable)?
- [ ] If so, has the new server API been stable on production for at
least one server release cycle? See
[here](https://www.notion.so/warpdev/How-to-add-a-new-full-stack-feature-8412cede405a4ec194b32bdd4b951035?pvs=4#73b202f939834b97ab1fbdf7fc82cd53)
for more details.

## Agent Mode
- [ ] Warp Agent Mode - This PR was created via Warp's AI Agent Mode

## Changelog Entries for Stable
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CHANGELOG-NEW-FEATURE: {{text goes here...}}
CHANGELOG-IMPROVEMENT: 
CHANGELOG-BUG-FIX: Fix macOS IME candidate popup positioning in code
editor panes so it anchors to the editor caret instead of stale
terminal/input positions.
CHANGELOG-BUG-FIX: 
CHANGELOG-IMAGE: {{GCP-hosted URL goes here...}}
CHANGELOG-OZ: {{text goes here...}}

Author: qubaitian

app/src/code/editor/view.rs

@@ -80,8 +80,8 @@ use warpui::{
     prelude::RectF,
     text::point::Point,
     units::Pixels,
-    AppContext, BlurContext, Element, Entity, FocusContext, ModelHandle, SingletonEntity, View,
-    ViewContext, ViewHandle, WeakViewHandle, WindowId,
+    AppContext, BlurContext, CursorInfo, Element, Entity, FocusContext, ModelHandle,
+    SingletonEntity, View, ViewContext, ViewHandle, WeakViewHandle, WindowId,
 };
 
 mod actions;
@@ -2335,6 +2335,18 @@ impl View for CodeEditorView {
         }
     }
 
+    fn active_cursor_position(&self, ctx: &ViewContext<Self>) -> Option<CursorInfo> {
+        let render_state = self.model.as_ref(ctx).render_state().as_ref(ctx);
+        let cursor_id = render_state.saved_positions().cursor_id();
+        let font_size = render_state.styles().base_text.font_size;
+
+        ctx.element_position_by_id(cursor_id.as_str())
+            .map(|position| CursorInfo {
+                position,
+                font_size,
+            })
+    }
+
     fn on_blur(&mut self, blur_ctx: &BlurContext, ctx: &mut ViewContext<Self>) {
         if blur_ctx.is_self_blurred() {
             ctx.notify();