feat: make headers self-contained

[sergiud]

No description provided.

[codecov-commenter]

Codecov Report

Attention: 42 lines in your changes are missing coverage. Please review.

Comparison is base (dfce35c) 59.14% compared to head (63f445a) 58.95%.

Files	Patch %	Lines
src/flags.cc	27.50%	1 Missing and 28 partials ⚠️
src/includes_unittest/glog_includes_raw_logging.cc	0.00%	6 Missing ⚠️
src/includes_unittest/glog_includes_logging.cc	0.00%	5 Missing ⚠️
src/includes_unittest/glog_includes_stl_logging.cc	0.00%	1 Missing ⚠️
src/includes_unittest/glog_includes_vlog_is_on.cc	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1030      +/-   ##
==========================================
- Coverage   59.14%   58.95%   -0.20%     
==========================================
  Files          18       23       +5     
  Lines        2541     2553      +12     
  Branches      907      912       +5     
==========================================
+ Hits         1503     1505       +2     
- Misses        694      706      +12     
+ Partials      344      342       -2     

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