Use .NET 4 CLR hosting API

[breyed]

This PR contains the remaining changes not applied from the previous PR, and a couple things I noticed when merging. The biggest fish is to use .NET 4 CLR hosting API; hence the title of the PR, but there are several other enhancements as well.

The PR is based on RickStrahl/wwDotnetBridge/master, so it seems like it should be easy to merge, but then again, GitHub says "Can’t automatically merge." I don't know if that's because of the size of the diff or some other reason. Hopefully, it will be painless. 🤞

This PR does not contain high priority features or fixes, but rather more subtle improvements, many of which were byproducts of my debugging efforts, but IMHO still well worth incorporating.

Enhancements fall into these categories:

wwDotnetBridge.prg

• Eliminate the workaround that had been needed for indexing in the parameter array. Corresponding changes also exist in the DotNetBridge and Tests projects.
• Use spaces for indentation (vs. a mix of tabs and spaces).

ClrHost

• For .NET Framework 4, don't rely on deprecated CLR hosting, but instead use the APIs designed for .NET 4.
• For CLR hosting, use a systematic approach to error handling. This catches previously ignored errors and shrinks the code to make the overall process easier to grok.

DotNetBridge

• Document that InvokeMethodAsync uses a thread-pool-thread rather than its own thread. It's important to say this because if lots of long-running async calls were attempted concurrently (usually a sign of a design problem), I think the thread pool could be exhausted.
• Use the new csproj style (much smaller and more readable XML). I updated wwDotNetBridge.sln accordingly.

Tests

• Display additional status.

[breyed]

We ran into some intermittent problems with the async approach to subscribing to events. After looking at how the async code is implemented, I saw that we didn't need to use the async subsystem, but could instead, call back into the event dispatcher directly. This removed the event wait loop as fixed the reliability problem.

[breyed]

I merged your latest commits into breyed/master so that you can pull in the remaining changes without conflicts. The primary update in my branch since your latest release is that events are now raised directly, rather than via InvokeMethodAsync. This avoids timing issues when unsubscribing.

My branch also contains various other minor changes that I'd made along the way. Let me know if any don't seem suitable for inclusion. I want to get to a point where my branch matches yours so that it's easier to make clear, narrow changes.

If you use GitHub for diffing, wwDotnetBridge.PRG might be annoying to look at, since one of the minor changes was fixing the mix of tabs and spaces to just spaces (which seems to be what you had intended). Fortunately, GitHub has a secret URL suffix ?w=1 to ignore whitespace.