functions TypeRegistry.shutdownFileSystemWatcherThread and FileSystemWatcher.shutdownAndWait

## Context

I integrate springloaded and embedded tomcat in [gretty gradle plugin](https://github.com/akhikhl/gretty).

## Problem

When stopping/restarting webapp under embedded tomcat with springloaded agent, tomcat issues warning:

```
The web application [/xyz] appears to have started a thread named [FileSystemWatcher: files=#1 cl=java.net.URLClassLoader@777d673c]
```

The warning is apparently related to the fact that FileSystemWatcher thread is still running, even when related classloader goes out of scope (as by webapp stop/restart),

## Solution

I need the new function `TypeRegistry.shutdownFileSystemWatcherThread` in order to deterministically shut down springloaded threads before webapp is stopped.