feat(indev): support read_preprocess_cb for indev, allow for preproce…

[bjsylvia]

…ss or user-customized gesture detection

A clear and concise description of what the bug or new feature is.

Notes

• Update the Documentation if needed.
• Add Examples if relevant.
• Add Tests if applicable.
• If you added new options to lv_conf_template.h run lv_conf_internal_gen.py and update Kconfig.
• Run scripts/code-format.py (astyle v3.4.12 needs to installed by running cd scripts; ./install_astyle.sh) and follow the Code Conventions.
• Mark the Pull request as Draft while you are working on the first version, and mark is as Ready when it's ready for review.
• When changes were requested, re-request review to notify the maintainers.
• Help us to review this Pull Request! Anyone can approve or request changes.

[kisvegabor]

Could you describe the purpose of this feature in more details?

FYI, we have added a gesture detection system a few weeks ago https://github.com/lvgl/lvgl/tree/master/examples/others/gestures

[bjsylvia]

The main consideration of this design is to support the system's ability to prioritize handling system key behaviors or custom gestures before the event is dispatched to the target component.

In this scenario, what the system needs are raw input events, rather than processed gestures or other events.

[kisvegabor]

So, let's say there is a normal PC keyboard. When a letter is pressed it's forwarded to the widgets normally. However when e.g. a volume up button is pressed something custom should happen. Is it a good example?

If so can it be handled in the normal read_cb like this?

void my_read_cb(lv_indev_t * indev, lv_indev_data_t * data)
{
   bool state;
   int32_t k = key_get(&state) 
   if(is_sys_key_action(k)) {
       sys_key_handle(k);
   } else {
      data.key = k;
      data.state = state;
   }
}

[bjsylvia]

The read_cb mainly cannot meet the following requirements:

1. read_preprocess_cb needs to provide a mechanism to interrupt the subsequent dispatch process to the component when necessary.
2. In the case of multiple instances, the read_preprocess_cb for each instance maybe different, some need to listen, some do not.
3. In terms of architecture, the common implementation of read_cb is in the lvgl driver layer, while read_preprocess_cb needs in the business or system layer.

So I introduced the read_preprocess_cb mechanism.