Restore functionality as mbed library

```
mkdir test && cd test
mbed new test
mbed add https://github.com/arduino/ArduinoCore-API
mbed add https://github.com/arduino/ArduinoCore-mbed
cat <<EOT >> main.cpp

int main() {
  pinMode(PA_0, OUTPUT);
  while (1) {
    digitalWrite(PA_0, HIGH);
    delay(100);
    digitalWrite(PA_0, LOW);
    delay(100);
  }
}
EOT

mbed compile -m TARGET -t GCC_ARM
```

Author: facchinm

.mbedignore

@@ -1,9 +1,11 @@
+cores/arduino/mbed.h
 cores/arduino/mbed/*
 cores/arduino/api/Stream.h
 cores/arduino/api/deprecated/Stream.h
 cores/arduino/main.cpp
-variants/*mbed_config.h
-variants/E*
-variants/M*
-libraries/micro*
-libraries/WiFi*
+cores/arduino/mbed/*
+cores/arduino/mbed*
+libraries/openamp*
+cores/arduino/USB/*
+variants/*
+libraries/*

cores/arduino/Arduino.h

@@ -23,10 +23,7 @@
 #if !defined(Arduino_h) && !defined(ARDUINO_LIB_DISCOVERY_PHASE)
 #define Arduino_h
 
-#if !defined(ARDUINO_AS_MBED_LIBRARY)
 #include "pinmode_arduino.h"
-#endif
-
 #include "api/ArduinoAPI.h"
 
 #if defined(__cplusplus)

cores/arduino/as_mbed_library/pinmode_arduino.h

@@ -0,0 +1,71 @@
+#pragma once 
+
+/* Define mock symbols to nullify PinMode definitions */
+#define PullNone            TempPullNone 
+#define PullUp              TempPullUp 
+#define PullDown            TempPullDown 
+#define OpenDrainPullUp     TempOpenDrainPullUp 
+#define OpenDrainNoPull     TempOpenDrainNoPull 
+#define OpenDrainPullDown   TempOpenDrainPullDown 
+#define PushPullNoPull      TempPushPullNoPull     
+#define PushPullPullUp      TempPushPullPullUp    
+#define PushPullPullDown    TempPushPullPullDown  
+#define OpenDrain           TempOpenDrain         
+#define PullDefault         TempPullDefault       
+
+#define INPUT           TempINPUT
+#define OUTPUT          TempOUTPUT
+#define INPUT_PULLUP    TempINPUT_PULLUP
+#define INPUT_PULLDOWN  TempINPUT_PULLDOWN
+
+/* Rename symbol PinMode into MbedPinMode for all the file PinNamesTypes.h
+ * Functions using PinMode should be redeclared with the correct PinMode symbol */
+#define PinMode MbedPinMode
+#include "PeripheralNames.h"
+#include "PinNamesTypes.h"
+#undef PinMode
+
+/* Rename symbol PinMode into ArduinoPinMode for all the file Common.h
+ * Functions using PinMode should be redeclared with the correct PinMode symbol */
+#define PinMode ArduinoPinMode
+#include "api/Common.h"
+#undef PinMode
+
+#undef PullNone         
+#undef PullUp           
+#undef PullDown         
+#undef OpenDrainPullUp  
+#undef OpenDrainNoPull  
+#undef OpenDrainPullDown 
+#undef PushPullNoPull   
+#undef PushPullPullUp    
+#undef PushPullPullDown  
+#undef OpenDrain         
+#undef PullDefault       
+
+#undef INPUT
+#undef OUTPUT
+#undef INPUT_PULLUP
+#undef INPUT_PULLDOWN
+
+/* Define the PinName symbol to be used in all the contexts */
+typedef enum {
+    PullNone          = TempPullNone,
+    PullUp            = TempPullUp,
+    PullDown          = TempPullDown,
+    OpenDrainPullUp   = TempOpenDrainPullUp,
+    OpenDrainNoPull   = TempOpenDrainNoPull,
+    OpenDrainPullDown = TempOpenDrainPullDown,
+    PushPullNoPull    = TempPushPullNoPull,
+    PushPullPullUp    = TempPushPullPullUp,
+    PushPullPullDown  = TempPushPullPullDown,
+    OpenDrain         = TempOpenDrain,
+    PullDefault       = TempPullDefault,
+    INPUT = TempINPUT,
+    OUTPUT = TempOUTPUT,
+    INPUT_PULLUP = TempINPUT_PULLUP,
+    INPUT_PULLDOWN = TempINPUT_PULLDOWN
+} PinMode;
+
+/* Redeclare Common.h functions with the updated PinMode */
+void pinMode(pin_size_t pinNumber, PinMode pinMode);

cores/arduino/as_mbed_library/pins_arduino.h

@@ -0,0 +1,2 @@
+#define PINS_COUNT 255
+#define NUM_ANALOG_INPUTS	4

cores/arduino/as_mbed_library/variant.cpp

@@ -0,0 +1,16 @@
+#ifdef ARDUINO_AS_MBED_LIBRARY
+
+#include "Arduino.h"
+#include "pinDefinitions.h"
+
+// generic variant
+
+PinDescription g_APinDescription[PINS_COUNT];
+
+void initVariant() {
+	for (int i = 0; i<PINS_COUNT; i++) {
+		g_APinDescription[i].name = (PinName)i;
+	}
+}
+
+#endif

cores/arduino/mbed.h

@@ -1,3 +1,5 @@
+#ifdef USE_ARDUINO_PINOUT
+
 #include "drivers/InterruptIn.h"
 #include "drivers/PwmOut.h"
 #include "drivers/AnalogIn.h"
@@ -35,3 +37,5 @@ inline PinName digitalPinToPinName(pin_size_t P) {
 #endif
 
 int PinNameToIndex(PinName P);
+
+#endif