Debugging slows down JavaScript execution 20x times

While working on PR-4 I realized that Truffle debugger support in NetBeans slows down execution 20x times. Without debugger the benchmark can execute in 150ms. With debugger it takes more than 3s. At current state the great Truffle debugging feature is not suitable for a demo.

To reproduce, you need:

• NetBeans 10 VC2
• JDK11
• graal-js-jdk11-maven-demo at revision 2f851ca6d922

Then you can debug the AppTest unit test and put a breakpoint to calls to eval, etc. Once the breakpoint is hit, remove it and continue. The rest of the execution will be slow - e.g. take more than 3s for each round.