core : Switch to spdlog for logging

[ManifoldFR]

• Add spdlog dependency
• multibody/RobotScene : move invalid_enum() back to cpp file
• [cmake] add spdlog dependency
• Use spdlog instead of SDL_Log(...)
• Format RobotSpec in spdlog
• runtime/main.cpp : process SPDLOG_LEVEL envar and set pattern
• core/Texture : add getter for name
• Remove deprecated header core/Renderer.h
• Some logging adjustments