Support PS/2 mouse 9-bit output with MOUSE_EXTENDED_REPORT

[dkao]

Description

Support the 8-bit + sign-bit output from PS/2 using MOUSE_EXTENDED_REPORT.
Also gives user code more range to scale mouse movement.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[drashna]

Honestly, it may be better to move the ps2 stuff over to the pointing device code, in general. It would simplify/solve a lot of this, I think.

[dkao]

Right, I was wondering why PS/2 mouse is a special case.
Does QMK still support only one pointing device? There are use cases that have a PS/2 mouse and some other pointing device.

[drashna]

It's mostly that way because they were added at different points, and I didn't have a ps2 device to test with.

That said, yeah, it's mostly just a single device only, at this point, but dasky has been working on making adding multiple devices a lot more seamless:
#20374

[freznel10]

It's mostly that way because they were added at different points, and I didn't have a ps2 device to test with.

That said, yeah, it's mostly just a single device only, at this point, but dasky has been working on making adding multiple devices a lot more seamless: #20374

been rocking #20374 and tried porting ps2 trackpoint to it but I've been getting weird results as I can't make RP2040 PS/2 PIO driver to play nice with it:( I will chuck this to my ignorance