Relocate matrix_scan_quantum tasks

[zvecr]

Description

Dependency for #15722.

Having 2 files which collect the various _tasks adds unnecessary complexity. While overall behaviour should be mostly the same, with this PR the order will have slightly changed.

Before:

1. scan matrix
2. master only tasks
3. matrix_scan_kb/matrix_scan_user
4. other tasks

After:

1. scan matrix
2. matrix_scan_kb/matrix_scan_user
3. master only tasks
4. other tasks

Given how the scan callbacks have little way in interaction with the other tasks, it should be fairly safe to change the order.

Also,

• led_matrix_task would previously be called twice on splits
• mid file hd44780.h include removed

Note: Future iterations are planned to further sort out the fragmentation shown by the tmk_core+quantum merge.

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).