[Keymap] I2C scanner (#8454)

* Add i2c scanner keymap

* Add bodge for chibios

* Fix readme title

* make chibios bodge a little cleaner

* fix typo in readme

keyboards/handwired/onekey/keymaps/i2c_scanner/readme.md

@@ -0,0 +1,36 @@
+# i2c_scanner
+
+Aiming to provide a more qmk friendly version of <https://playground.arduino.cc/Main/I2cScanner/>
+
+> This very simple ~~sketch~~ keymap scans the I2C-bus for devices. If a device is found, it is reported to the ~~Arduino serial monitor~~ console.
+
+
+## Flashing
+
+Pick a target that is aligned to the MCU you want to test:
+
+```console
+make handwired/onekey/elite_c:i2c_scanner:flash # also 32u4 + dfu bootloader
+make handwired/onekey/promicro:i2c_scanner:flash
+make handwired/onekey/teensy_2:i2c_scanner:flash
+
+# ChibiOS is currently 'best effort' and might not report accurate results
+make handwired/onekey/proton_c:i2c_scanner:flash
+```
+
+others might work with additional configuration.
+
+## Usage
+
+Output is viewable through a compatible tool <https://docs.qmk.fm/#/newbs_testing_debugging?id=debugging-tools>.
+
+You can change the wires, and plug-in I2C devices while the i2c_scanner is running.
+
+The output of the console will look like this:
+
+```
+Listening:
+Scanning...
+  I2C device found at address 0x20
+done
+```