Check in Arduino API directory to avoid symlink (#176)

Fixes #171

Under Windows, it is very hard to make a symlink and by default git won't
make one to the Arduino API directory, causing annoying build errors.

Avoid the issue by duplicating the ArduinoAPI directory explicitly and using
CI to verify that there are no differences between the two.

.github/workflows/pull-request.yml

@@ -20,7 +20,7 @@ jobs:
     - name: Run codespell
       uses: codespell-project/actions-codespell@master
       with:
-        skip: ./pico-extras,./ArduinoCore-API,./libraries/SdFat,./libraries/Adafruit_TinyUSB_Arduino,./libraries/LittleFS/lib,./tools/pyserial,./pico-sdk,./.github,./docs/i2s.rst
+        skip: ./pico-extras,./ArduinoCore-API,./libraries/SdFat,./libraries/Adafruit_TinyUSB_Arduino,./libraries/LittleFS/lib,./tools/pyserial,./pico-sdk,./.github,./docs/i2s.rst,./cores/rp2040/api
         ignore_words_list: ser,DOUT
 
 # Consistent style
@@ -44,6 +44,10 @@ jobs:
         ./tests/restyle.sh
         # If anything changed, GIT should return an error and fail the test
         git diff --exit-code
+    - name: Check Arduino API copy is clean
+      run: |
+        git submodule update --init ./ArduinoCore-API
+        diff -r ./cores/rp2040/api ./ArduinoCore-API/api
 
 # Build all examples on linux (core and Arduino IDE)
   build-linux: