Windows: Set "intelliSenseMode" property in c_cpp_properties.json file to "gcc-arm"

PlatformIO should set "intelliSenseMode" property in c_cpp_properties.json file to "gcc-arm".

Since PlatformIO uses gcc-arm, the Intellisense should use gcc-arm as well. During startup the IntelliSense mode is changed and following message is displayed:

[11/23/2020, 8:41:51 AM] For C++ source files, IntelliSenseMode was changed from “gcc-x64” to “gcc-arm” based on compiler args and probing compilerPath: “C:/Users/itsme/.platformio/packages/toolchain-gccarmnoneeabi/bin/arm-none-eabi-gcc.exe”

Changing the c_cpp_properties.json manually to "gcc-arm" also work temporary as it is auto generated and platformio overwrites and set it back to "gcc-x64".