Migrate mousekey to quantum

[zvecr]

Description

Types of Changes

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

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).

[uqs]

This broke my build.

Compiling: quantum/mousekey.c                                                                      quantum/mousekey.c: In function ‘move_unit’:
quantum/mousekey.c:135:35: error: ‘mouse_timer’ undeclared (first use in this function)
  135 |     } else if (mousekey_repeat && mouse_timer) {
      |                                   ^~~~~~~~~~~
quantum/mousekey.c:135:35: note: each undeclared identifier is reported only once for each function it appears in
quantum/mousekey.c: At top level:
quantum/mousekey.c:149:7: error: conflicting types for ‘mk_wheel_interval’
  149 | float mk_wheel_interval = 1000.0f / MOUSEKEY_WHEEL_INITIAL_MOVEMENTS;
      |       ^~~~~~~~~~~~~~~~~
quantum/mousekey.c:68:9: note: previous definition of ‘mk_wheel_interval’ was here
   68 | uint8_t mk_wheel_interval    = MOUSEKEY_WHEEL_INTERVAL;
      |         ^~~~~~~~~~~~~~~~~
quantum/mousekey.c: In function ‘wheel_unit’:
quantum/mousekey.c:156:35: error: ‘mouse_timer’ undeclared (first use in this function)
  156 |     } else if (mousekey_repeat && mouse_timer) {
      |                                   ^~~~~~~~~~~
 [ERRORS]

mouse_timer is only declared under ifdef MK_KINETIC_SPEED but then later used indiscriminately. Easy enough to fix. But the other error is more problematic. In any case, my mouse cursor speed is now absolutely effed.

My config was working fine before:

// KC_ACL0 et al work when held.                                                                       
#define MK_COMBINED
#define MOUSEKEY_WHEEL_INTERVAL 30                                                                     

[uqs]

Filed issue#12241 so this comment doesn't get lost.