[libcxx] [test] Fix MSVC warning C4389 "signed/unsigned mismatch", part 8/12.
Add static_cast<std::size_t> when comparing distance() to size().
These replacements were performed programmatically with regex_replace():
const vector<pair<regex, string>> reg_fmt = {
{ regex(R"(assert\((\w+)\.size\(\) == std::distance\((\w+, \w+)\)\))"), "assert($1.size() == static_cast<std::size_t>(std::distance($2)))" }, { regex(R"(assert\(distance\((\w+\.begin\(\), \w+\.end\(\))\) == (\w+)\.size\(\)\))"), "assert(static_cast<std::size_t>(distance($1)) == $2.size())" }, { regex(R"(assert\(std::distance\((\w+\.\w*begin\(\), \w+\.\w*end\(\))\) == (\w+)\.size\(\)\))"), "assert(static_cast<std::size_t>(std::distance($1)) == $2.size())" },
};
Also, include <cstddef> when it wasn't already being included.