[Bullet] InputEvent in StaticBody always return index 0

[Hromon]

Godot version:

Mono 3.2.3 and 3.2.4

OS/device including version:

Win 10 64

Issue description:

InputEvent in StaticBody always return 0 index shape for ConcavePolygonShape...

Minimal reproduction project:

Example.zip

[pouleyKetchoupp]

This is a known issue with Bullet and not specific to Mono, it doesn't happen with Godot Physics.
See #39767.

MRP with gdscript:
ConcavePolygonShapeIndex.zip

In 3.2.3, it actually returns the triangle index instead of shape index when using Bullet.

PR #42882 enforces indices to be 0 (instead of triangle indices) and documents this limitation with Bullet, but it would be nice to fix it (probably upstream).
CC @AndreaCatania