fuse: add ACL support (Linux)

[ThomasWaldmann]

Junie (AI) experiment + some fixes the AI was not clever enough for.

But, tests fail - anyone wants to review this?

[codecov[bot]]

Codecov Report

:x: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review. :warning: Please upload report for BASE (master@6a83ea1). Learn more about missing BASE report. :warning: Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/borg/platform/__init__.py	66.66%	1 Missing :warning:
src/borg/platform/base.py	50.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #8843   +/-   ##
=========================================
  Coverage          ?   82.05%           
=========================================
  Files             ?       77           
  Lines             ?    13515           
  Branches          ?     2004           
=========================================
  Hits              ?    11090           
  Misses            ?     1759           
  Partials          ?      666           

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