[FeatureRequest]: add length state to pulsed filament sensor

[scyomantion]

Is your feature request related to a problem? Please describe.

I would like to use the ERCF MMU on my printer. It has a pulse generating filament sensor that can be used to measure the length as the filament is loaded and unloaded into the hotend. In theory, this can be used to monitor the process, such as detecting if a filament is grabbed for loading, loading the filament close to the hotend extruder so that it can grab the filament, checking if there is any movement as the extruder pushes the filament forward. At the moment it is not possible to check the distance the filament has moved with this filament sensor in macros.

Describe the solution you propose.

It would be great if the pulsed filament sensor (and any other that has information about how much the filament is moving) could export a total length state that could be used in macros.

Describe alternatives you've considered

A workaround is to configure the pulsed filament sensor as a pulsed trigger that calls the trigger event. There it is possible to increment a global variable with the total counts. This only works at low speeds, as at higher speeds there will be missing trigger events because the pulses count faster than the events can be executed.

Provide any additional context or information.

I have tried adding this feature to the code myself and it helps me a lot. I think it would be useful for other people as well. I have added my patch files for 3.4-dev, but I think it needs some code cleanup.
I could make a pull request if you like.
canlib_3.4-dev.patch
rrf_3.4-dev.patch