Make Result accessible via evmc_result reference

[yperbasis]

With .raw() method the evmc::Result can be passed to functions that just observe evmc_result and don't care about ownership. Something like:

void on_result(const evmc_result& res) {
  // use res somehow
}

void blah() {
  evmc::Result res{EVMC_SUCCESS, 1000, 0};
  on_result(res.raw()); // fine after this PR
}

[codecov]

Codecov Report

Merging #686 (eac92d2) into master (44fc118) will not change coverage.
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Additional details and impacted files

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