graphics/unpaper: Update to 7.0.0

Changelog:

• Tests now compare a golden file by counting the bytes that differ between it and the result. This allows non-byte-perfect calculations to be executed and still not fail the tests. This is required as fused multiply-add instructions can increase precision and thus deviate from the base C code, when using floating-point arithmetic.

• Build is now provided by Meson, replacing the Autotools based build system introduced in 0.4, 10½ years ago.

• Compatibility expanded to ffmpeg-5 (and newer versions), which is the current widely available release.

https://github.com/unpaper/unpaper/releases/tag/unpaper-7.0.0

PR: 270218