Use the same `".selection"` attribute for both curve and point domains, instead of a different name for each. The attribute can now have either boolean or float type. Some tools create boolean selections. Other tools create float selections. Some tools "upgrade" the attribute from boolean to float. Edit mode tools that create selections from scratch can create boolean selections, but edit mode should generally be able to handle both selection types. Sculpt mode should be able to read boolean selections, but can also and write float values between zero and one. Theoretically we could just always use floats to store selections, but the type-agnosticism doesn't cost too much complexity given the existing APIs for dealing with it, and being able to use booleans is clearer in edit mode, and may allow future optimizations like more efficient ways to store boolean attributes. The attribute API is usually used directly for accessing the selection attribute. We rely on implicit type conversion and domain interpolation to simplify the rest of the code. Differential Revision: https://developer.blender.org/D16057