Added '@' prefix when exporting directives in Apollo.

[danielreynolds1]

Added '@' prefix when exporting directives using a type rather than a name.
Modified tests to ensure both use cases are snapshotted.

(Partially) Closes #7799

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.34%. Comparing base (4cbe8b9) to head (36f7844).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7812   +/-   ##
=======================================
  Coverage   74.33%   74.34%           
=======================================
  Files        2871     2871           
  Lines      149797   149797           
  Branches    17416    17416           
=======================================
+ Hits       111346   111360   +14     
+ Misses      32652    32635   -17     
- Partials     5799     5802    +3     

Flag	Coverage Δ
unittests	74.34% <ø> (+<0.01%)	⬆️

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