Add compilation count threshold triggering AppDomain recycle

When compiling CSX based functions, each new compilation will result in a new dll. If there are too many of these within a single AppDomain, it can cause problems - e.g. sandbox memory limits on page-file backed files. This has caused issues in long lived host instances.

We could experiment to find the right threshold and implement a simple compilation counter triggering an AppDomain restart.

Another possibility is to put intelligent caching in place such that when files/dependencies haven't changed, a cached compilation is used.