ls parser speed improvements, reworked

[PaulWay]

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Complete Description of Additions/Changes:

This is an update for my previous ls parser speed improvements work, after the removal of 'raw_entry' by @xiangce.

Main speed improvements are:

• Once the format of the directory has been found, use the same function to parse all lines in that directory.
• In parsing subfunctions, put data directly into the dirent's dictionary.
• Only parse name -> link if the dirent is actually a link.
• Handle files first when adding to the files/dirs/specials lists.
• Ignore obviously malformed lines.
• Faster and easier to read logic for partly-formed directory listings with dirname not first line.

Readability improvements are:

• Functions for name handling, SELinux context handling, major,minor/size/date handling.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.51%. Comparing base (05eb089) to head (c942700).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4408      +/-   ##
==========================================
+ Coverage   77.50%   77.51%   +0.01%     
==========================================
  Files         744      744              
  Lines       41574    41571       -3     
  Branches     6667     6665       -2     
==========================================
+ Hits        32220    32223       +3     
+ Misses       8319     8315       -4     
+ Partials     1035     1033       -2     

Flag	Coverage Δ
unittests	77.50% <100.00%> (+0.01%)	:arrow_up:

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