Add wp_pointer_warp_v1 protocol support

[zakissimo]

Closes #3988.

Adds support for the wp_pointer_warp_v1 staging protocol (wayland-protocols 1.45).
Niri's pinned Smithay already includes the server-side handler from
Smithay#1757; this PR is the compositor
wiring + validation policy + the niri-side helpers.

Validation policy

Implements the protocol's three "should" rules with lenient (KWin-style) semantics:
focus + bounds, no button_count > 0 requirement. The protocol says "honor it if the
surface has pointer focus, including when it has an implicit pointer grab" — "including"
reads as "focus is sufficient; implicit grab is one valid case", not as a requirement.
Most legitimate SetCursorPos-class callers (Wine apps, mouselook recentering,
drag-completion, menu navigation) happen outside a button-down, so the strict reading
rejects most of them.

Reference implementations

(Per @YaLTeR's request in #3988.)

• KWin (commit, Sept 2024).
  Validation in src/pointer_input.cpp:152-164 — focus + bounds, no grab requirement. Lenient.
• Mutter (commit, July 2025).
  Validation in meta_wayland_pointer_can_warp — adds button_count > 0. Strict.

Implementation overview

• Two free helpers in src/utils/mod.rs:
  • get_surface_toplevel_coords — walks the subsurface chain accumulating offsets via
    SubsurfaceCachedState.location. Parallel to Smithay's existing get_popup_toplevel_coords
    (which handles xdg_popup chains).
  • get_surface_size — reads RendererSurfaceState::surface_size().
• impl PointerWarpHandler for State in src/handlers/mod.rs: serial check via
  pointer.last_enter(), surface-local bounds check, find_window_and_output →
  window-rect → output-global four-term composition, self.move_cursor(target).
• New per-window window_visual_rectangle(id) -> Option<Rectangle<f64, Logical>> at all
  four layout layers (floating/scrolling/workspace/monitor), parallel to the existing
  active_window_visual_rectangle. Dispatches monitor → workspace → (floating | scrolling).
• Field + init + delegate macro for PointerWarpManager in src/niri.rs and
  src/handlers/mod.rs.

Testing

Verified end-to-end with Wine MR !10830
— the matching client-side winewayland.drv patch.

• SetCursorPos called 12 times by a test program (3 laps × 4 corners of a square).
• Niri side: registry binds the global; every warp validated and honored; cursor lands on
  each target.
• Wine side: every GetCursorPos returns the requested position — full roundtrip works.

Tested both nested (winit backend) and as a real session.