fix(core, windows): allow user to override MSVC_RUNTIME_MODE

[lightrabbit]

Description

1. Fixed CMakeLists to allow user to override MSVC_RUNTIME_MODE

Related Issues

google/flutter-desktop-embedding#587
Some users need to build flutter applications that use a static runtime. Modifying this part of the CMake configuration file can provide an easy way for users to override the runtime configuration.

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Breaking Change

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[Lyokone]

Thanks for this :)