Add toolchain file to optimize MSVC-based release builds

[fredemmott]

• use 'hybrid CRT' to keep it dependency-free on Win10+ without the full size of static linking
• add default MSVC release optimizations to RelWithDebInfo

refs #704

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Testing:

cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_TOOLCHAIN_FILE=D:/vcpkg/scripts/buildsystems/vcpkg.cmake -DVCPKG_CHAINLOAD_TOOLCHAIN_FILE=D:/openfpgaloader/cmake/Toolchain-x86_64-w64-msvc-redist.cmake -DVCPKG_TARGET_TRIPLET=x64-windows-static

cmake --build . --parallel --config RelWithDebInfo

On my v1.1.1 branch, this gets me a 2.5MB exe that only depends on:

• WS2_32.dll (winsock2, specifically ntohs()
• KERNEL32.dll
• ucrtbase.dll (~ libc)

... and also gives me ~ 20MB of debug symbols, separate to the exe:

I then used this to re-flash a ModRetro Chromatic with customized firmware:

[fredemmott]

Just for comparison, here's the current mingw build (~ 4MB):

... and the mingw ucrt build (~ 4MB):

By comparison, this toolchain + MSVC allows 'just download the exe', more suitable for integration with other programs (e.g. FlashGBX) - and it's ~ half the size of the mingw binaries that depend on libftdi/libusb