The Clay Strips brush calculates a brush plane and local matrix to use
for a cube distance test. This test is done based on the sampled plane
center, not the current cursor position.
To make the node mask match this brush area, this commit reworks the
node mask calculation similar to the Plane brush, also calculating the
plane normal and plane center to be used later.
Finally, the relative radius scale of the brush is fixed to be a
constant SQRT(3) to ensure that the cube influence area is fully
circumscribed by the spherical distance query.
Further work here can change the type of BVH distance query done to
reduce the number of nodes processed by the brush.
Resolves#123768
Related to #84169
Pull Request: https://projects.blender.org/blender/blender/pulls/137371
900b26181a