Add next tapping record user callback

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Description

Add a new get_next_tapping_record() function that allows user space read access to the next buffered tapping key. This can provide more granular control to tap-hold decision function based on that key.

Example:

bool get_permissive_hold(uint16_t keycode, keyrecord_t *record) {
    keyrecord_t next = get_next_tapping_record();
    // row > 3 on a 3x5_2 split is the right side
    // enable permissive hold for left-shift with right-side keys
    if (keycode == LSFT_T(KC_A) && next.event.key.row > 3 && next.event.pressed) {
        return true;
    }
    return false;
}

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).

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The same information can be extracted with pre_process_record_user (#20584). Closing this to avoid cluttering action_tapping with more shims.