VW MQB: alpha longitudinal doesn't support cancel from main switch

[jyoung8607]

Describe the bug

A subset of Volkswagen family vehicles have no standalone cancel button, instead overloading this function onto the momentary-contact main switch button. openpilot operates as-expected on all these vehicles when using stock ACC, including cancel spam to disengage on gas. However, it doesn't currently implement cancel functionality for these cars under alpha longitudinal, so brake (or gas, if enabled) is the only normal way to disengage.

• [ ] Cleanup and align GRA_ACC_01 in vw_mqb_2010.dbc with current data sources
• [ ] Panda checksum, counter, and rate enforcement for GRA_ACC_01 now that receiving it is safety-relevant
• [ ] Sense main switch type (momentary contact vs latching) from GRA_ACC_01.GRA_Typ_Hauptschalter
• [ ] If type is momentary contact, cancel on rising edge of GRA_ACC_01.GRA_Hauptschalter

Provide a route where the issue occurs

bbc2fa573509b5ff|2023-07-02--00-06-58

openpilot version

master

Additional info

In North America, Volkswagen family vehicles with steering wheel buttons MY2018 and older, there is a dedicated Cancel button. There is a separate button to invoke the ADAS features menu at the tip of the turn signal stalk.

For vehicles MY2019 and newer, the ADAS features menu button at the tip of the turn stalk goes away, and moves to where the Cancel button was. Cancel functionality is overloaded onto the momentary-contact main switch button, directly above.

Vehicles outside of North America may be missing the Cancel button as well, in favor of a mode-switch button that toggles between a speed limiter mode and actual cruise control (standard or adaptive as-equipped).