Closes https://github.com/zed-industries/zed/issues/45553

## Summary

When using applications that hide the terminal cursor (e.g., via ANSI
escape sequence `\e[?25l`), the IME candidate window appeared at the
bottom-left of the screen, and the composition text was not displayed at
all. This affects tools like Claude Code that hide the cursor during
operation.

The root cause was that cursor position calculation was skipped when the
cursor shape was `Hidden`. This fix separates cursor visibility from IME
position calculation by always computing cursor bounds for IME
positioning.

## Movies

### Zed 0.218.6


https://github.com/user-attachments/assets/a66d569a-178d-4bca-a577-fcc65e9fd2c4

### With this fix


https://github.com/user-attachments/assets/456323d1-6c18-45ea-88e8-fb5375c00f98

Release Notes:

- Fixed IME candidate window and composition text position in terminal
when cursor is hidden