Add support for WLCS keyboard

[tarek-y-ismail]

What's new?

• Adds support for WLCS's keyboard interface
• Bumps WLCS support from 2 to 4 (3 was for an optional feature we didn't need)

How to test

• Build mir from this branch: cmake -B build && cmake --build build
• Check out the code for Keyboard support wlcs#407, or main if it was merged, and build it
• Run WLCS's new keyboard tests, assuming it was built in build: ./build/wlcs <path to mir>/build/lib/miral_wlcs_integration.so --gtest_filter=KeyboardTest*

Checklist

• Tests added and pass: in WLCS
• Adequate documentation added
• (optional) Added Screenshots or videos

[Copilot]

Pull request overview

This PR adds keyboard support to Mir's WLCS (Wayland Conformance Test Suite) integration, enabling keyboard-related conformance tests. The implementation follows the established patterns used for pointer and touch device integration.

Changes:

• Adds FakeKeyboard implementation following the same pattern as FakeTouch
• Implements keyboard event synthesis (key down/up) using Mir's input synthesis APIs
• Bumps WLCS protocol version from 2 to 4 to enable keyboard interface support

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/mir_test_framework/test_wlcs_display_server.cpp	Implements FakeKeyboard struct, keyboard event handlers (key_down/key_up/destroy), create_keyboard method with DeviceObserver synchronization, and updates WLCS version to 4
include/test/miral/test_wlcs_display_server.h	Adds create_keyboard() method declaration to TestWlcsDisplayServer interface

[github-actions]

TICS Quality Gate

✔️ Passed

No changed files applicable for TICS analysis quality gating.

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[tarek-y-ismail]

Looks like the latest version of WLCS with keyboard support is not packaged outside of Ubuntu.