Export file system facade to be used in tests

[uhafner]

Otherwise we cannot write integration tests in the analysis-model project.

[github-actions]

☀️   Quality Monitor

   🚦   Tests: 98% successful (✔️ 103 passed, 🙈 2 skipped)
   〰️   Line Coverage: 92% (61 missed lines)
   ➰   Branch Coverage: 91% (19 missed branches)
     Mutation Coverage: 80% (80 survived mutations)
   💪   Test Strength: 85% (58 survived mutations in tested code)
     CheckStyle: No warnings
     PMD: No warnings
     SpotBugs: No bugs
   🐛   Error Prone: No bugs
   🚫   Revapi: No warnings
     OWASP Dependency Check: No vulnerabilities
   🌀   Cyclomatic Complexity: 376 (total)
   💭   Cognitive Complexity: 173 (total)
   📏   Lines of Code: 4043 (total)
   📝   Non Commenting Source Statements: 1257 (total)
   🔭   Access to foreign data: 88 (total)
   🔗   Class cohesion: 71.43% (maximum)
   📤   Fan out: 278 (total)
   📲   Number of accessors: 14 (total)
   ⚖️   Weight of a class: 100.00% (maximum)
   📐   Weighted method count: 375 (total)
   ➿   N-Path Complexity: 455 (total)

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🚧   Error Messages

Quality Monitor Errors:
No matching report files found when using pattern ''! Configuration error for 'Revapi'?

Created by Quality Monitor v1.14.0 (#f3859fd). More details are shown in the GitHub Checks Result.