Update HitData position docs (#17833)

# Objective

Updates the now inaccurate position docs
Fixes #17832 

## Solution

From
`The position of the intersection in the world, if the data is available
from the backend.`
To
`The position reported by the backend, if the data is available.
Position data may be in any space (e.g. World space, Screen space, Local
space), specified by the backend providing it.`

## Testing

uhh reading :)

Author: bytemunch

crates/bevy_picking/src/backend.rs

@@ -105,7 +105,8 @@ pub struct HitData {
     /// distance from the pointer to the hit, measured from the near plane of the camera, to the
     /// point, in world space.
     pub depth: f32,
-    /// The position of the intersection in the world, if the data is available from the backend.
+    /// The position reported by the backend, if the data is available. Position data may be in any
+    /// space (e.g. World space, Screen space, Local space), specified by the backend providing it.
     pub position: Option<Vec3>,
     /// The normal vector of the hit test, if the data is available from the backend.
     pub normal: Option<Vec3>,