Improve Debugging experience by copying sources

Copying sources next to the binary allows gdb to automatically detect
the sources. One still has to start up gdb from this directory though.

Follow up to #12294

1. 1. Before this patch one needs to:

```
cd target/getting-started-1.0-SNAPSHOT-native-image-source-jar
gdb ../getting-started-1.0-SNAPSHOT-runner
```

To make `gdb` detect the sources without the need of executing gdb's `directory` or `set directories` commands.

1. 1. After this patch one needs to:

```
cd target
gdb getting-started-1.0-SNAPSHOT-runner
```

which should be more intuitive.

Since this is not a major improvement we might as well skip it.