vcpkg does not include IPC feature

[paleolimbot]

In microsoft/vcpkg#46029 I tried to add the IPC feature but it doesn't quite work because

• the vcpkg version is at 0.6.1, which is the last "release" but is also too old for us (if I remember correctly we need a newer version because of the verify code)
• Finding flatcc isn't quite supported because flatcc doesn't provide cmake or pkgconfig. We can almost certainly use find_library() or the installed directory for this.

set(NANOARROW_IPC_OPTION OFF)
set(NANOARROW_FLATCC_ROOT_DIR_OPTION "")
if("ipc" IN_LIST FEATURES)
    set(NANOARROW_IPC_OPTION "-DNANOARROW_IPC=ON")
    set(NANOARROW_FLATCC_ROOT_DIR_OPTION = "-DNANOARROW_FLATCC_ROOT_DIR=${CURRENT_INSTALLED_DIR}")
endif()

vcpkg_cmake_configure(
    SOURCE_PATH "${SOURCE_PATH}"
    OPTIONS
        -DNANOARROW_INSTALL_SHARED=${NANOARROW_INSTALL_SHARED}
        -DNANOARROW_DEBUG_EXTRA_WARNINGS=OFF
        ${NANOARROW_IPC_OPTION}
        ${NANOARROW_FLATCC_ROOT_DIR_OPTION}
)

I also found that setting the LIB_DIR option for flatcc doesn't quite work (unsurprising because we never test it!)