[SRU] Cannot render long EULA pages with llvmpipe

[Yao Wei]

[ Impact ]

 * This bug causes EULA page cannot be displayed when the EULA page is too long, and is using llvmpipe renderer to render, due to the texture dimension limit of 16384px.

 * The fix tries to address this limit by splitting PDF rendering into multiple GtkDrawingArea.

[ Test Plan ]

 * Use an OEM image where problem could occur, for example Dell image, on a QEMU/KVM environment, where llvmpipe renderer is the default, finish installation and ensure the problem is reproducible.

 (For versions where OEM customization does not exist, I guess it is okay to install EULA files package and test it. I have not tried it yet.)

 * Update the package to a proposed version.

 * Test that the problem is no longer reproducible. Note that using "gnome.initial-setup=1" in kernel cmdline can reenter initial setup page.

 * For regression testing:

    * Test the same page and same EULA file with Intel GPU and NVIDIA GPU.

    * Test without EULA file (the EULA page would be skipped).

    * Test language switching. The EULA file should be switched to an appropriate file when the file exists, if not a fallback EULA file should be displayed.

    * Test language switching without EULA file.

[ Where problems could occur ]

 * The problem itself might not get fixed.

 * If EULA page causes gnome-initial-setup to crash, user might not be able to create an account on the system.

[ Other Info ]

 * Normally this issue shouldn't happen, as for OEM team, we ensure that the system is using a correct GPU driver.

[Yao Wei (medicalwei)]

Salsa MPs:
resolute: https://salsa.debian.org/gnome-team/gnome-initial-setup/-/merge_requests/74
noble: https://salsa.debian.org/gnome-team/gnome-initial-setup/-/merge_requests/75
oracular: https://salsa.debian.org/gnome-team/gnome-initial-setup/-/merge_requests/76