Track filesystem accesses during Probe.configure()

Probes currently only run whenever their configure content or input properties change. If a probe accesses files and the files are updated later on, the probe is not re-executed. In many cases, users want probes to automatically re-run whenever input files are updated. They do not want to explicitly --force-probe-execution.

Suggestion:
1. Add a files property similar to what Products have

• Track changes in those files similar to what products do
• Re-run the probe whenever these files are updated

2. Maybe track file accesses during configure through the Qbs file APIs automatically and add another property trackFileAccesses to explicitly switch that behavior off