Add editor layout preset menu

[yasufumi-nakata]

Fixes #100.

I can't use the GitLab instance from this machine, so I'm submitting this through the GitHub mirror.

This replaces stale/conflicting PR #365 with a fresh branch against current master.

Summary:

• Add a top-level Layout editor menu with preset apply, reload, and save-current-layout actions.
• Wire the menu through the editor GUI and CMake targets.
• Extend LayoutManager to load YAML layout presets from EditorAssets/Configuration/Layouts, support external ImGui ini payloads through ImGuiIniPath, preserve full ini data on save, and update existing presets by display name.
• Move the default layout payload into EditorAssets/DefaultLayout/imgui.ini and point the default preset YAML at it.

Verification:

• git diff --check
• Confirmed default layout manifest references DisplayName and ImGuiIniPath, and that EditorAssets/DefaultLayout/imgui.ini exists.
• Focused clang++ -std=c++17 -fsyntax-only check for LayoutManager.cpp and GUI_Menu_Layout.cpp using local stubs for unavailable external dependencies.

Known local build blocker:

• Full CMake configure still cannot run in this checkout because ThirdParty/vcpkg/scripts/buildsystems/vcpkg.cmake is missing and no Unix Makefiles build program is configured (CMAKE_MAKE_PROGRAM unset).