Make build work with Java 17

The problem is that the API package isn't exported:

```
java.lang.IllegalAccessError: class org.moditect.deptective.DeptectivePlugin (in unnamed module @0x646007f4) cannot access class com.sun.tools.javac.api.BasicJavacTask (in module jdk.compiler) because module jdk.compiler does not export com.sun.tools.javac.api to unnamed module @0x646007f4
```