Add weak refs on reading rows/cols.

[tzarc]

Description

Allow for keyboards to override implementations full-port reads without messing with the rest of the scanning logic, and without requiring a full custom matrix.

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).

[mtei]

I am not opposed to this change.

However, there is something that I feel is insufficient in this change.

If a keyboard author implements matrix_init_pins() and matrix_read_cols_on_row() in his own way, does he need the configuration macros MATRIX_ROW_PINS and MATRIX_COL_PINS? And does he need pin_t row_pins[MATRIX_ROWS] and pin_t col_pins[MATRIX_COLS]?

It would be nice to have some explanation of these points in the documentation.

[tzarc]

Fair enough. Will try and add something to #13064.