Handle multi-part-template-block output from Parsoid's linter

The messaging is a bit tricky. In some cases, the flag is set
because the output involves a single template and some top-level
content -- not multiple templates always.

Ex: '{{1x|<div>}}foo</span>'

In this case, the entire content is considered template-affected
because of DOM structuring reasons. This wikitext will generate
lint errors with multi-part-template-block template info.

In production usage, however, the probability is quite high that
multiple templates will be involved. This is usually because of
tables that are constructed with multiple templates, for example.

So, if we want to fudge and hand-wave a bit, the i18n message can
say that the output came from multiple templates.

Bug: T162920
Change-Id: I35cee6787800b03724856775fdf53991ae8e8125