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/configuration.h

@@ -114,6 +114,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define CARDKB_ADDR 0x5F
 #define TDECK_KB_ADDR 0x55
 #define BBQ10_KB_ADDR 0x1F
+#define MPR121_KB_ADDR 0x5A
 
 // -----------------------------------------------------------------------------
 // SENSOR