Blender Git Loki

GPencil: Fix wrong python API for Point weights

The old property never worked as expected because it was impossible expose the data as props.

Now, there are two methods to handle this: weight_get and weight_set

Example use:
```import bpy
ob = bpy.context.active_object
gpd = ob.data
gps = gpd.layers[0].frames[0].strokes[0]
i = 0
print("Weightsn================================")
for pt in gps.points:
gps.points.weight_set(vertex_group_index=0, point_index=i, weight=0.5)
i +=1

i = 0
for pt in gps.points:
weight = gps.points.weight_get(vertex_group_index=0, point_index=i)
print(weight)
i +=1
```

Reviewed By: brecht

Maniphest Tasks: T84967

Differential Revision: https://developer.blender.org/D10177
b3f989