Don't apply UI scaling (dpi override) to safe inset areas / IME areas (#1084)

* Don't apply UI scaling (dpi override) to safe inset areas / IME areas

Scaling those areas doesn't make sense, as it can lead to empty space
(extra unnecessary padding) on the border of the IME or the device inset area,
which looks bad and is basically objectively wrong

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Centralize native/physical/layout DPI conversion on `CxWindow`, and use it at platform boundaries for window geometry, safe-area insets, input coordinates, soft keyboard spacing, clipboard and selection overlays, and camera preview rects.

Add runtime `set_window_dpi_override` support that rescales all window-local metrics and emits `WindowGeomChange`.

* Fix pre-existing iOS and Android build breaks

iOS (platform/src/os/apple/ios/ios.rs): five `CxOsOp` arms had edits
that landed one match-arm late, so each block referenced bindings only
in scope on the preceding arm. Re-home them:

- `WindowGeomChange` now applies `native_window_geom_to_layout` (the
  two stray lines previously sat inside the `Paint`/`prepared` arm).
- `ShowTextIME` now converts `pos` via `layout_vec2d_to_native_points`
  (previously lodged inside the `SyncImeState` destructure pattern).
- `ShowClipboardActions` now converts `rect` / `keyboard_shift` to
  native points (previously appended to `ShowSelectionHandles`).
- `ShowSelectionHandles` / `UpdateSelectionHandles` now convert `start`
  and `end` (the `Update` arm had no conversion, and the `Show` arm's
  conversion was actually the clipboard one).
- `FullscreenWindow` / `NormalizeWindow` drop the bogus `start` / `end`
  conversions that didn't belong there.

Android (platform/src/ime.rs): `android_jni::to_java_configure_keyboard`
matches on `InputMode::None` and `ReturnKeyType::{Next, None, Previous,
Google, Yahoo, Join, Route, Continue, EmergencyCall}` — variants that
exist on the `ime_improvements` branch (commit 3dc039f0a) but weren't
pulled into this branch. Add them to the enum definitions so the
android target compiles.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>