Fix parsing of years ending in zero

Assume year precision instead of automagically converting
and assuming precision of decade, millenium, etc.

Require explicit precision option for setting those precisions.

In Wikibase, precision can be set via advanced options in the
time widget, via the api (e.g. bot edit), or providing certain
specific text input (e.g. '19. century').

Note: We should be flexible in the future on what to parse,
such as '19th century'. (see bug 64545)

Bug: 64537