When a cron name is invalid, it wasn't necessarily clear why. This
change-set improves the error message to inform the user of the valid
characters in a cron name.
This PR removes the use of the custom `utc_now` function in favor of the
`chrono` implementation. It resolves #22864.
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Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>
This PR adds unstable `Deno.cron` API to trigger execution of cron jobs.
* State: All cron state is in memory. Cron jobs are scheduled according
to the cron schedule expression and the current time. No state is
persisted to disk.
* Time zone: Cron expressions specify time in UTC.
* Overlapping executions: not permitted. If the next scheduled execution
time occurs while the same cron job is still executing, the scheduled
execution is skipped.
* Retries: failed jobs are automatically retried until they succeed or
until retry threshold is reached. Retry policy can be optionally
specified using `options.backoffSchedule`.
