Simplify GetTime
Summary:
The implementation of GetTime is confusing:
- The value returned by GetTime is assumed to be equal to GetTime<std::chrono::seconds>(). Both are mockable and the only difference is return type, the value itself is equal. However, the implementation does not support this assumption.
- On some systems, time_t might be a signed 32-bit integer (https://en.cppreference.com/w/c/chrono/time), thus breaking in the year 2038, whereas GetTime<std::chrono::seconds> does not. Also, time_t might be -1 "on error", where "error" is unspecified.
- GetTime<std::chrono::seconds> calls GetTimeMicros, which calls GetSystemTime, which calls std::chrono::system_clock::now, which doesn't have the above issues. See https://en.cppreference.com/w/cpp/chrono/system_clock/now
- GetTimeMicros and the internal-only GetSystemTime will likely be renamed (to clarify they are the non-mockable non-monotonic system time) or removed in the future to be replaced by appropriate std::chrono::time_point<Clock> getters.
Fix all issues by:
- making GetTime() an alias for GetTime<std::chrono::seconds>().count().
- inlining the needed parts of GetSystemTime directly instead of needlessly increasing the function call stack with functions that are likely to be removed in the future.
This is a backport of core#24871
Depends on D11790
Test Plan: ninja all check-all
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D11791