Special:PagesWithProp: Do not show very long or binary values

It already looks rather silly when querying for 'templatedata' prop
from the TemplateData extension (e.g. [1]), it will start looking much
worse once Ie66b0dd6 in TemplateData is merged (which makes it store
the props gzip-compressed).

Do not show very long (over 1 kB) or binary (containing a null byte)
values; instead display a helpful message and size.

Changing the display format slightly, it's now "Page: <propvalue-or-message>"
instead of "Page (<propvalue-or-message>)", because the helpful
messages themselves include parentheses.

[1] https://en.wikipedia.org/wiki/Special:PagesWithProp?propname=templatedata

Bug: 51888
Change-Id: Ib2db241a117b06faee2426c8ea9ae18eab499e08
Merge "Special:PagesWithProp: Do not show very long or binary values"