Add boringssl header file for tquic.h.

[codecov-commenter]

Codecov Report

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

Project coverage is 95.13%. Comparing base (402223f) to head (e5aaa45).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #254 +/- ## =========================================== - Coverage 95.13% 95.13% -0.01% =========================================== Files 49 49 Lines 33188 33188 =========================================== - Hits 31574 31572 -2 - Misses 1614 1616 +2 ```

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