chore: 添加 UI_CORE_BUILD_DEMO 选项以可选编译 ui-demo-uix.exe

[WuJunkai2004]

添加该选项后，用户使用cmake 拉取core-ui作为依赖并编译时，可以关闭 ui-demo-uix.exe的编译，加快构建过程

include(FetchContent)

FetchContent_Declare(
    core-ui
    GIT_REPOSITORY https://github.com/ghboke/core-ui.git
    GIT_TAG        v1.7.0
    GIT_SHALLOW    TRUE
)

set(UI_CORE_STATIC ON CACHE BOOL "" FORCE)
set(UI_CORE_BUILD_STATIC_ARCHIVE OFF CACHE BOOL "" FORCE)

set(UI_CORE_BUILD_DEMO OFF CACHE BOOL "" FORCE)

FetchContent_MakeAvailable(core-ui)