This commit adds an initial STL import node, the first of the nodes from the current Google Summer of Code Project [0]. The importer is refactored to output a mesh pointer, and a node is added to wrap around the importer. The node supports error messages from the importer. A new experimental option is added to hide the nodes by default until they're ready to be exposed generally. 0: https://devtalk.blender.org/t/gsoc-2024-geometry-nodes-file-import-nodes/34482) Pull Request: https://projects.blender.org/blender/blender/pulls/122418