Preserve ENHANCED_KEY for direct key events (Alt up, F7 down)

[TheJesper]

Summary of the Pull Request

WindowEmperor::_dispatchSpecialKey intercepts Alt key-up (and F7 key-down) to handle the window menu before XAML sees them. These events get forwarded through IDirectKeyListener::OnDirectKeyEvent, but the extended-key bit from lParam was dropped along the way. Without it, TermControl can't distinguish RightAlt from LeftAlt on release, so a RightAlt key-up produces an INPUT_RECORD identical to LeftAlt. The key press works fine because it goes through the regular XAML _KeyHandler path where CorePhysicalKeyStatus.IsExtendedKey is available.

Fix: thread an extended bool through the OnDirectKeyEvent chain and set ControlKeyStates::EnhancedKey when true - same thing the regular key path already does. Changed signature: OnDirectKeyEvent(vkey, scanCode, down, extended).

References and Relevant Issues

Closes #18120

Detailed Description of the Pull Request / Additional comments

The asymmetry happens because the emperor intercepts Alt-up for system menu handling - it needs to swallow it before XAML turns it into a menu activation. That interception path (_dispatchSpecialKey) only extracted the virtual key, scan code, and up/down state from lParam, ignoring bit 24 (the extended-key flag). This PR extracts that bit and passes it through.

Validation Steps Performed

Built two copies locally (x64 Debug, VS 2026 / SDK 10.0.26100), registered with Add-AppxPackage -Register, ran on Windows 11. Used a small ReadConsoleInputW repro tool with win32-input-mode enabled (\x1b[?9001h), pressing RightAlt and LeftAlt on a Swedish keyboard layout (where RightAlt is AltGr, so Windows translates it to Ctrl+Alt - hence the (auto) LeftCtrl events).

Before (parent commit 079d1cc) - RightAlt release loses its identity:

pressed     reported    action   EK    note
----------  ----------  -------  ----  ------
RightAlt    LeftCtrl    press    0     (auto)
RightAlt    RightAlt    press    1
RightAlt    LeftCtrl    release  0     (auto)
RightAlt    LeftAlt     release  0     <-- wrong, should be RightAlt
LeftAlt     LeftAlt     press    0
LeftAlt     LeftAlt     release  0

After (this branch) - works correctly:

pressed     reported    action   EK    note
----------  ----------  -------  ----  ------
RightAlt    LeftCtrl    press    0     (auto)
RightAlt    RightAlt    press    1
RightAlt    LeftCtrl    release  0     (auto)
RightAlt    RightAlt    release  1     <-- correct
LeftAlt     LeftAlt     press    0
LeftAlt     LeftAlt     release  0

Also added InputTest::Win32KeyEventsRetainEnhancedKey which checks that win32-input-mode encodes the flag correctly for both press and release of RightAlt. Passes locally.

PR Checklist

• Closes ENHANCED_KEY flag missing when releasing RightAlt #18120
• Tests added/passed
• Documentation updated
• Schema updated (if necessary)

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