MPR121 Touch IC Based Keypad Input Module (#5103)

Implements an input driver utilising the MPR121 Touch IC and is compatible with common MPR121 keypad PCB's.

- Implements a "candybar" phone style 12-key keypad
  - multiple taps to rotate through the character set
  - longpress for navigation keys
  - keymap to allow arbitrary routing of MPR121 pin to button configuration
  - extendable to other key functions
- Integrates with the existing kbI2cBase implementation
- Works with CannedMessageModule Freetext mode
- Can be used with common MPR121 boards, such as https://www.amazon.com/MPR121-Capacitive-Keyboard-Buttons-Sensitive/dp/B083R89CHB/ref=sr_1_6
- Of use for PCB based radios, where some form of low surface area low component freetext input is required, but also without consuming too many IO pins.
- Tested on a T3S3 connected to Wire1 (Second) interface.
  - Demonstration of functionality: https://youtu.be/UI6QP6nGvhY

src/input/MPR121Keyboard.h

@@ -0,0 +1,56 @@
+// Based on the BBQ10 Keyboard
+
+#include "concurrency/NotifiedWorkerThread.h"
+#include "configuration.h"
+#include <Wire.h>
+#include <main.h>
+
+class MPR121Keyboard
+{
+  public:
+    typedef uint8_t (*i2c_com_fptr_t)(uint8_t dev_addr, uint8_t reg_addr, uint8_t *data, uint8_t len);
+
+    enum MPR121States { Init = 0, Idle, Held, HeldLong, Busy };
+
+    MPR121States state;
+
+    int8_t last_key;
+    uint32_t last_tap;
+    uint8_t char_idx;
+
+    String queue;
+
+    MPR121Keyboard();
+
+    void begin(uint8_t addr = MPR121_KB_ADDR, TwoWire *wire = &Wire);
+
+    void begin(i2c_com_fptr_t r, i2c_com_fptr_t w, uint8_t addr = MPR121_KB_ADDR);
+
+    void reset(void);
+
+    void attachInterrupt(uint8_t pin, void (*func)(void)) const;
+    void detachInterrupt(uint8_t pin) const;
+
+    void trigger(void);
+    void pressed(uint16_t value);
+    void held(uint16_t value);
+    void released(void);
+
+    uint8_t status(void) const;
+    uint8_t keyCount(void) const;
+    uint8_t keyCount(uint16_t value) const;
+
+    bool hasEvent(void);
+    char dequeueEvent(void);
+    void queueEvent(char);
+
+    uint8_t readRegister8(uint8_t reg) const;
+    uint16_t readRegister16(uint8_t reg) const;
+    void writeRegister(uint8_t reg, uint8_t value);
+
+  private:
+    TwoWire *m_wire;
+    uint8_t m_addr;
+    i2c_com_fptr_t readCallback;
+    i2c_com_fptr_t writeCallback;
+};