impl(oauth2): `project_id()` for credential decorators

[coryan]

Part of the work for #14112

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This change is 

[codecov[bot]]

Codecov Report

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

Project coverage is 93.25%. Comparing base (2bc2215) to head (9cc103f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14240   +/-   ##
=======================================
  Coverage   93.25%   93.25%           
=======================================
  Files        2210     2210           
  Lines      192870   192918   +48     
=======================================
+ Hits       179860   179910   +50     
+ Misses      13010    13008    -2     

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