Fix anchor biases for completion replacement ranges (esp slash commands) (#32262)

Closes #32205

The issue was that in some places the end of the replacement range used
anchors with `Bias::Left` instead of `Bias::Right`. Before #31872
completions were recomputed on every change and so the anchor bias
didn't matter. After that change, the end anchor didn't move as the
user's typing. Changing it to `Bias::Right` to "stick" to the character
to the right of the cursor fixes this.

Release Notes:

- Fixes incorrect auto-completion of `/files` in text threads (Preview
Only)

crates/inspector_ui/src/div_inspector.rs

@@ -715,7 +715,7 @@ fn completion_replace_range(snapshot: &BufferSnapshot, anchor: &Anchor) -> Optio
 
     if end_in_line > start_in_line {
         let replace_start = snapshot.anchor_before(line_start + start_in_line);
-        let replace_end = snapshot.anchor_before(line_start + end_in_line);
+        let replace_end = snapshot.anchor_after(line_start + end_in_line);
         Some(replace_start..replace_end)
     } else {
         None