[unsupported-object-issue-fix part2] Skip unsupported object names in list output

[gargnitingoogle]

Description

Skips unsupported object names during all file operations in GCSFuse mounts (e.g. listings, renames, and deletions). It also add debug logs on both types of above skips.

GCS supports objects of path-type <bucket>/<path1>//<path2>
and treats it different from <bucket>/<path1>/<path2>, while they are both the same in linux filesystem.
GCSFuse being a POSIX-compliant file-system only support the latters and throws error on former. This error can disallow the listing of all directories in the parent directory i.e. <path1>.

The current change ignores the listing/deletion/renaming of prefixes (directory names) which are empty such
as "/" above to ignore the error and logs the above event as a warning.

This is on top of #2561 (utilities) and is followed up in #2011 (which adds e2e tests for this change).

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual -
   • GCS bucket structure: 1. <bucket>//a, 2. <bucket>/b/c, 3. <bucket>/d//e .
   • GCSFuse mount command: gcsfuse --implicit-dirs --log-file=$logfile --debug_fuse --log-format=text $bucket $mountpath
   • Without the fix,

     ls -R $mountpath
     ls: reading directory $mountpath: Input/output error
     cat $logfile
     - No warning/error log -
     rm -rfv $mountpath/*
     - No log -

   • With the fix,

         ls -R $mountpath
         $mountpath:
         total 0
         b
         d
     
         $mountpath/b:
         total 0
         c
     
         $mountpath/d:
         total 0
         
         cat $logfile
         ...
         Ignored following unsupported prefixes: [/]
         Ignored following unsupported prefixes: [d//]
         ...
     
         rm -rfv $mountpath/*
         
         
         ...

2. Unit tests - NA
3. Integration tests - With run as presubmit.

[gargnitingoogle]

Presubmit tests passed: logs

[ashmeenkaur]

Still need to take a look at the tests

[codecov]

Codecov Report

Attention: Patch coverage is 80.95238% with 16 lines in your changes missing coverage. Please review.

Project coverage is 77.55%. Comparing base (5ae03ff) to head (97bab99).

Files with missing lines	Patch %	Lines
internal/fs/inode/dir.go	83.87%	7 Missing and 3 partials ⚠️
internal/fs/fs.go	80.00%	3 Missing and 1 partial ⚠️
internal/fs/inode/base_dir.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1876      +/-   ##
==========================================
+ Coverage   77.47%   77.55%   +0.08%     
==========================================
  Files         110      110              
  Lines       15705    15785      +80     
==========================================
+ Hits        12167    12242      +75     
- Misses       3016     3020       +4     
- Partials      522      523       +1     

Flag	Coverage Δ
unittests	77.55% <80.95%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.