Move Wasmtime for .NET to the Wasmtime repo.

This moves the Wasmtime for .NET implementation to the Wasmtime repo.

Wasmtime for .NET is a binding of the Wasmtime API for use in .NET.

crates/misc/dotnet/examples/hello/hello.wat

@@ -0,0 +1,8 @@
+(module
+  (type $t0 (func))
+  (import "" "hello" (func $.hello (type $t0)))
+  (func $run
+    call $.hello
+  )
+  (export "run" (func $run))
+)