fix(tao): follow the caret with the Windows IME candidate window

[kdroidFilter]

Windows half of #558. Linux is untouched — the issue stays open for the GTK / Wayland text-input side.

Summary

• WindowsTaoPlatformContext now overrides startInputMethod the way the macOS host does: it keeps an input session for the focused BasicTextField and pushes focusedRectInRoot() to IMM32. Compose's default is awaitCancellation() with no IME spot, which is why the candidate list — and the OS-drawn composition string — sat at the client area's top-left instead of on the caret.
• New platform/windows/ime.rs exposes nativeSetImeRect, setting both IMM32 forms. Tao's own set_ime_position only sets a COMPOSITIONFORM, which positions the inline composition window; the candidate list is placed from the CANDIDATEFORM. The caret box is passed as a CFS_EXCLUDE area so the candidate list never covers the text being edited, and both forms anchor at the caret's top-left (same as winit and as Tao's set_ime_position_physical) so the composition string stays on the caret's line.
• nativeCancelImeComposition drops any in-flight composition when the input session ends, so a pending candidate window does not linger over unfocused content nor commit into whatever gains focus next.
• The caret rect is clamped to textClippingRectInRoot(). It is root-relative and goes negative once the field scrolls out of the viewport, which would fling the candidate window off the window. A clamp rather than Rect.intersect + overlaps, because a caret rect can legitimately be zero-width and no overlap test accepts a degenerate rect.
• Adds the Win32_UI_Input_Ime feature to the windows crate.

No coordinate conversion is needed: the scene covers the whole client area — the custom title bar is drawn inside it and reports no platform inset — so scene-root physical pixels are already client pixels. Both new externs are Java→native only, so no GraalVM reachability metadata is required.

Also refreshes two example API baselines that had drifted (Compose lambda name hashes in rect-stress-demo, plus a first dump for widget-demo). Unrelated to the fix, carried along from an apiDump.

Test plan

• cargo build --release --target x86_64-pc-windows-msvc clean, no new warnings
• build.bat produces win32-x64 + win32-aarch64 DLLs; both JNI symbols exported
• compileKotlin, ktlintCheck, detekt, apiCheck pass
• tao-demo launches without an UnsatisfiedLinkError
• Manual, with a CJK IME installed (Microsoft Pinyin or Japanese IME): focus a BasicTextField in tao-demo, type nihao / konnichiha — the candidate window sits under the caret and follows it when the window moves or resizes
• Manual: the underlined composition string renders on the caret's line, not one line below it
• Manual: start a composition, click into another field — composition and candidate window disappear, and the pending text is not inserted into the new field
• Manual: scroll the focused field out of the viewport mid-composition — the candidate window stays clamped to the visible text region

Marked draft: the IMM32 behaviour above still needs a run on a machine with a CJK IME installed.