glib: Add poppler_page_set_render_antialias(PopplerPage*, cairo_antialias_t)

The `pdftocairo` command-line tool has an `-antialias` option
that configures the anti-aliasing mode used when rasterizing text and shapes
(for example when the output is PNG). This is based on calling the internal
`CairoOutputDev::setAntialias` method.

In the glib API, `poppler_page_render` is also based on `CairoOutputDev`
but there is no call to `setAntialias` so `CAIRO_ANTIALIAS_DEFAULT`
(set in `CairoOutputDev`’s constructor) is always used regardless
of how the cairo context was configured before being passed to
`poppler_page_render`.

This fills the gap by keeping an antialiasing mode in each `PopplerPage`
object, adding a setter for it, and calling `CairoOutputDev::setAntialias`
in each rendering function.
6 jobs for poppler_page_set_render_antialias in 3 minutes and 33 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #316889
build

00:02:39

passed #316894
build_android

00:00:47

passed #316890
build_clang_libcpp

00:02:32

passed #316893
build_clazy

00:03:32

passed #316892
build_mingw64_fedora

00:03:15

passed #316891
build_ubuntu_16_04

00:01:23