GM Camera ACC ICE: ECM respects different brake signal than camera

This is a ***stock ACC*** route where the user pressed the brake and caused an ACC fault we alerted for. It appears that the camera uses what we found for the Bolt, a single bit signal: `ECMEngineStatus->BrakePressed` as it stayed engaged until the ECM faulted. However the ECM might look at `ECMAcceleratorPos->BrakePedalPos` or `EBCMBrakePedalPosition->BrakePedalPosition`. These bugs are ridiculous!

I performed extensive tests to find an appropriate brake signal for the Bolt, so this looks like it might only apply for ICE GMs. Perhaps this only surfaces when ACC is braking itself as the user is adding little brake pressure compared to what is already being applied, and the ECM looks at the position.


dc7716b32bf25574/2024-05-24--18-30-20

Start with the logged stock ACC route dc7716b32bf25574/2024-05-24--18-30-20 and compare ECMEngineStatus->BrakePressed with ECMAcceleratorPos->BrakePedalPos and EBCMBrakePedalPosition->BrakePedalPosition during the fault. Determine which signal the ICE GM ECM actually uses, then verify the corresponding ACC behavior and update the relevant signal definition or handling once the correct target is established.

Written by the indexing model from the issue text.