- mytime: max/min configure with UTC tz, convert to local tz during process starting, convert it to session tz before checking bound.
- time: so `check()`/`add()` need force pass `StatementContext` parameter.
- builtin_time: pass `StatementContext` from `b.ctx.sessionVars` into check/add.
- dump: also set timezone for StatementContext with UTC.
- *_test/mock: fix test case, make mock context with stmt TimeZone.
- add testcase for checkTimestamp and mytime convert timezone.
Truncate error make be treated as warning, we should handle it in `BinaryLiteral.ToInt`.
And compare BinaryLiteral directly instead of converting to uint64 because that the compare function doesn't have statement context.
