Update Magnum for ASCII PLY import and artifact-free text rendering

[mosra]

Another month+ worth of Magnum updates, this time containing two important usability features:

• The StanfordImporter and StlImporter plugins now delegate to Assimp for ASCII files instead of failing the import. Which brings the best of the two worlds -- I don't need to suffer through implementing an ASCII PLY or STL parser myself, and you don't need to suffer with slow import of binary PLY and STL files by defaulting to Assimp instead. In particular, Fix receptacle import when multiple importers are present. habitat-lab#1869 can be reverted after this PR is merged, and everything should continue to work.
• Text rendering artifacts that started happening after an update to the new and more efficient TextureTools::AtlasLandfill atlas packer are now gone again. In particular, the one-pixel glyph padding that was enabled for example in --[BE Week] Better Attributes Handle search efficiency; Viewer.cpp/Viewer.py text render fixes #2279 is done by default now. Explanation of the behavior and rationale for the new default is here.

Besides that, the following changes are worth mentioning:

• A new Debug::hex modifier to conveniently print integer values as hexadecimal. As a drive-by optimization, instances of the Debug class now occupy 16.67% less memory.
• The SceneGraph library is now capable of rendering more than 65k objects at once. The original limitation was due to a 16-bit type used internally, however there's enough free padding bytes to make it 32-bit without enlarging size of scene graph objects in memory.
• Containers::StaticArray is now trivially copyable and also usable in constexpr contexts. In practice that means better optimization opportunities for the compiler, IIRC Habitat isn't making any extensive use of this type anywhere.
• The GL::Mesh could draw from vertex buffers larger than 4 GB before, now it can draw from index buffers larger than 4 GB as well. I've already hit the 4 GB vertex buffer limit with batch renderer before, it's just a matter of time when it happens with indices too, so better be prepared.
• The Magnum CMake Find modules were updated to properly support the case where each project is installed in a different prefix, unblocking one Habitat use case: Consider switching from the legacy Find*.cmake modules to install(TARGETS ... EXPORT ...) mosra/magnum-integration#105
• The StbImageImporter now uses NEON on ARM machines, such as the new Macs, which may cause image import to be slightly faster.
• In addition to a WebPImporter there's now a WebPImageConverter as well, together with support for the WebP format in both the glTF importer and exporter. Mentioning just in case you'd have use for a format that's both lossless and lossy and can achieve a better compression ratio than PNG or JPEG. The prebuilt tool binaries have this plugin enabled now as well.

(Sorry, I deleted the PR template by accident. Tests are 🟢 on my end, that mypy failure wasn't me.)

Also mentioning @aclegg3 -- can't add you as a reviewer for some reason.

[aclegg3]

Thanks @mosra, I'm working on the CI issue here: #2356

[aclegg3]

Tests pass, so assuming all the build changes are good. :)
Thanks, mosra!
Also, CI lint issue should be resolved on main.

[0mdc]

Thank you!