Add unsupported directory substrings . and ..

[gargnitingoogle]

Description

This is an addition on top of #1876 . This adds ., .., ./, ../, /./ and /../ to the list of unsupport object names (or substrings) in Cloud Storage Fuse.

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - Yes
2. Unit tests - Added new tests accordingly. All tests passed locally.
3. Integration tests - Tested through presubmit.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.65%. Comparing base (077bb7f) to head (7aa8ad9).

Additional details and impacted files

@@                                    Coverage Diff                                     @@
##           gargnitin/fix-unsupported-directory-list/add-e2e-tests    #2001      +/-   ##
==========================================================================================
+ Coverage                                                   71.56%   71.65%   +0.09%     
==========================================================================================
  Files                                                          99       99              
  Lines                                                       10795    10795              
==========================================================================================
+ Hits                                                         7725     7735      +10     
+ Misses                                                       2724     2716       -8     
+ Partials                                                      346      344       -2     

Flag	Coverage Δ
unittests	71.65% <ø> (+0.09%)	⬆️

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