C# objects need to be collected and finalised on Host finalisation

[GooberMan]

The basic flow of memory usage in C# goes like this:

• Allocate a Host object
• Call a function which creates an ImportedFunction object stored in a static variale; or allocate a bound object which creates an ImportedClass object
• Do your thing
• Close your program
• Garbage collector finalises whatever it wants first, usually not in reverse order of allocation
• Host is destroyed somewhere, which kills all C++ side allocations and things like memory alloc/dealloc function pointers
• ImportedFunction/Class gets finalised, and accesses bad memory

This is clearly rubbish.

The solution is to force all ImportedFunction/Class objects to finalise when the host finalises, before binderoo_host_destroy is called. The current plan for the solution is to add each ImportedFunction/Class to a WeakReference list inside the Host. This will require making the Host object a singleton - which it is in C++ code anyway so no problem there. When the Host finalises, resolving those weak references and manually invoking Dispose on them will clean up all required C++ handles before the host itself gets finalised.