add a define PICK_PASS when picking algorithm is used

[mickae1]

Feature

I would like to modify the code in MetadataPickingPipelineStage.js

to just add this line :

  shaderBuilder.addDefine(
    "PICK_PASS",
    undefined,
    ShaderDestination.BOTH,
  );

this will help user/me to know that the vertex shader is used for drill_pick by example, and i need to make the line wider by example.