Mac support

[jonyMarino]

Based in #142 from @R2D2-3PO

This pull request introduces several improvements to the build system and Unreal integration, focusing on enhanced platform support (especially for macOS), improved dependency handling, and more robust scripting. The changes ensure that required libraries are correctly staged and linked across platforms, add flexibility for using prebuilt dependencies, and improve script reliability for project file generation.

Build system and dependency management:

• macOS OpenSSL handling: Adds a custom target to explicitly stage the OpenSSL crypto archive for Unreal, resolving Homebrew symlinks to avoid build machine dependencies.
• ONNX Runtime flexibility: Allows specifying a prebuilt ONNX Runtime package for macOS via ONNXRUNTIME_ROOTDIR or environment variable, with validation and fallback to fetching if not provided.
• Platform-specific Unreal library linking: Updates ProjectAirSim.Build.cs to robustly check for required libraries (like OpenSSL and ONNX Runtime) on macOS, and to conditionally add the lvmon library only if it exists, across all platforms. Also, improves include path management for dependencies. [1] [2] [3] [4] [5] [6] [7]

Conditional linking of lvmon:

• Adds conditional linking of the lvmon library in multiple CMake targets and Unreal build scripts, only including it for debug builds and when the library is present. [1] [2] [3] [4] [5] [6]

Build script improvements:

• Cross-platform VS Code project generation: Updates the VS Code project generation script to detect the correct Unreal Engine script for macOS or Linux, improves error handling, and fixes path resolution to be more robust. Also, adapts the sed command for launch configuration fixes to support both macOS and Linux. [1] [2] [3]

These changes collectively improve the developer experience and reliability of building and running the project across different platforms, especially macOS.