tests: Add script to annotate llvm-cov report html

[pdobacz]

This is a python utility to annotate the coverage report from llvm-cov automatically. Not sure yet if this belongs here or in a separate repo, or not at all, pushing it temporarily to a branch here until we decide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.37%. Comparing base (31bf211) to head (841ffee).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1364   +/-   ##
=======================================
  Coverage   81.37%   81.37%           
=======================================
  Files         151      151           
  Lines       13367    13367           
  Branches     3191     3191           
=======================================
  Hits        10877    10877           
  Misses        346      346           
  Partials     2144     2144           

Flag	Coverage Δ
eest-develop	90.27% <ø> (ø)
eest-develop-gmp	22.53% <ø> (ø)
eest-legacy	15.58% <ø> (ø)
eest-legacy-silkpre	24.83% <ø> (ø)
evmone-unittests	75.95% <ø> (ø)

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Components	Coverage Δ
core	94.07% <ø> (ø)
tooling	83.43% <ø> (ø)
tests	73.12% <ø> (ø)

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