This commit refactors the `tiles.html` include file so that when the
`site.tiles-source` is pages, pages with `show_tile: false` set in their
Front Matter are not counted as having been shown. Prior to this commit,
such pages were iterated over in the `for` loop, consuming a loop
iteration from the `site.tiles-count` counter.
Put another way, say you have set `tiles-count` to 6, and you have a
total of 10 pages. Of these ten pages, six have `show_tile` set to
`false`. The natural expectation would be that the home page layout
would display four tiles (10 - 6 = 4), but in fact, the exact number of
page tiles shown would depend on the specific lexicographical ordering
of the `site.html_pages` array, which could result in fewer than four
page tiles being shown.
This commit fixes the issue by excluding pages with `show_tile` set to
`false` first, and only then iterating over the remaining pages.