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/detect/ScanI2C.cpp

@@ -31,8 +31,8 @@ ScanI2C::FoundDevice ScanI2C::firstRTC() const
 
 ScanI2C::FoundDevice ScanI2C::firstKeyboard() const
 {
-    ScanI2C::DeviceType types[] = {CARDKB, TDECKKB, BBQ10KB, RAK14004};
-    return firstOfOrNONE(4, types);
+    ScanI2C::DeviceType types[] = {CARDKB, TDECKKB, BBQ10KB, RAK14004, MPR121KB};
+    return firstOfOrNONE(5, types);
 }
 
 ScanI2C::FoundDevice ScanI2C::firstAccelerometer() const