Support changing lane width, lane number across different maps

[pengzhenghao]

Does this feature is allowed now? This might be useful in MARL unprotected intersection!

@lqy0057 @Edwardhk

[pengzhenghao]

Modification and checklist:

1. Each block can have different lane width/num (rather than a map-level specification)
2. The zombie vehicle should behave correctly (since at the intersection part where the lane width/num change suddenly, we have no idea what would happen for the zombies at that time.)
3. The road should switch smoothly in observation space (in old state observation, we have many dimensions describing "the distance to left edge of the road" and so on, we should make them transit smoothly)

[pengzhenghao]

This should be an important feature in the PGDriveV3 envs (which is a formal extension to PGDriveV2!)

We need to push forward the research on generalization! Picking up PGDriveV2 and find the reason what creates the performance gap!