[Core] Split support for pointing devices. (#15304)

* Draft implementation

* formatting

* fix combined buttons

* remove pimoroni throttle

* sync pointing on a throttle loop with checksum

* no longer used

* doh

Co-authored-by: Drashna Jaelre <[email protected]>

* switch pimoroni to a cpi equivalent

* add cpi support

* allow user modification of seperate mouse reports

* a little tidy up

* add *_RIGHT defines.

* docs

* doxygen comments

* basic changelog

* clean up pimoroni

* small doc fixes

* Update docs/feature_pointing_device.md

Co-authored-by: Drashna Jaelre <[email protected]>

* performance tweak if side has usb

* Don't run init funtions on wrong side

* renamed some variables for consistency

* fix pimoroni typos

* Clamp instead of OR

* Promote combined values to uint16_t

* Update pointing_device.c

Co-authored-by: Drashna Jaelre <[email protected]>
Co-authored-by: Nick Brassel <[email protected]>

docs/feature_split_keyboard.md

@@ -266,6 +266,14 @@ This enables transmitting the current OLED on/off status to the slave side of th
 
 This enables transmitting the current ST7565 on/off status to the slave side of the split keyboard. The purpose of this feature is to support state (on/off state only) syncing.
 
+```c
+#define SPLIT_POINTING_ENABLE
+```
+
+This enables transmitting the pointing device status to the master side of the split keyboard. The purpose of this feature is to enable use pointing devices on the slave side. 
+
+!> There is additional required configuration for `SPLIT_POINTING_ENABLE` outlined in the [pointing device documentation](feature_pointing_device.md?id=split-keyboard-configuration).
+
 ### Custom data sync between sides :id=custom-data-sync
 
 QMK's split transport allows for arbitrary data transactions at both the keyboard and user levels. This is modelled on a remote procedure call, with the master invoking a function on the slave side, with the ability to send data from master to slave, process it slave side, and send data back from slave to master.