Investigate asset editing without loading .NET assemblies

Is your feature request related to a problem? Please describe.
Loading assemblies to edit asset is quite problematic:

• Compilation issues
• Missing dependencies
• Side-effects (ctor, etc.)
• Crash/stability
• Reload takes time and affect lot of objects

Describe the solution you'd like
Instead of loading real objects, one approach would be to use custom fake object that are based on reflection.
We would still need to load actual object for displaying stuff (i.e. scene editor) but we could do that out-of-process.

Likely issues or problem to deal with if taking this approach:

• dynamic/proxy: possibly heavy, lack of code completion (might be mitigated: https://github.com/dotnet/roslyn/issues/15974#issuecomment-268297743)
• default values in .ctor are gone
• huge amount of work

Note that it is just a proposal that will need further investigation, and it might not be such a good idea in practice. Created issue to keep track of some details that were discussed in Discord.

No files, tests, or entry points are named. Begin by evaluating the reflection-based fake-object proposal against the listed assembly-loading problems and risks, then determine whether the out-of-process approach supports asset editing and scene display; done means a documented feasibility decision and scoped follow-up work.