Allow for rasterization of filter effects after page 1 of PDF output

This MR removes the hidden assumption that the document contains only one page, which somehow managed to survive the multipage revolution tucked in an obscure corner of the "rasterize filter effects" code.

In a nutshell, the rasterization step no longer clips the item's bounding box to the document bounds. Since these "document bounds" correspond to just the first/default page, the rasterization step is no longer aborted prematurely on subsequent pages.

Note that any items that are placed on a non-first page have already passed a collision check with that page, so the removed early return isn't actually needed. Therefore, this change shouldn't have an appreciable impact on performance.

This MR also adds a regression test: a CLI test producing multi-page PDF output of which the second page is analysed.

Fixes #3214 (closed)