[Sync-En] localtime, parse, parseToCalendar: correct the offset semantics (#4820)

[lacatoire]

Fixes #1213

Sync with EN commit 8871302d240f124f7e9dabac85862e31bf97b442.

• Correct offset parameter documentation: it holds the position at which parsing ended (success or failure), not -1 on success
• localtime/parse: also fail immediately if offset is negative
• parseToCalendar: only fails immediately if offset > strlen (exempts -1)
• localtime: mark up parameter references ($value/$parse_pos → parameter tags)
• localtime: qualify tm_yday as 1-based (unlike localtime() which is 0-based)
• parse: describe formatter as object, not resource