Add support for decoding WebP images

[notjosh]

Hiya 👋

I was hoping to use WebP in a project, and noticed (via #575) that the image-webp project has been published now. This PR adds support for the project within resvg.

As noted in #575 there may be performance issues - I haven't tested extensively. However in my use case, it saves a step of converting .webp images to a compatible format, so even a slow(ish) implementation is an overall positive. With that in mind, it feels like a step forward for resvg to support WebP, even if there's still room in future for their (pre-1.0) project to improve.

[RazrFalcon]

Looks good to me. All we have to do now is to ask them nicely to stop using thiserror.

[RazrFalcon]

https://github.com/image-rs/image-webp/issues/66

[RazrFalcon]

Looks like we need a MSRV bump as well.

[RazrFalcon]

Ok, waiting for 0.1.3 and I'm ready to merge.

[adamJLev]

any updates on this? would be great to have webp support ❤️

[LaurenzV]

Still waiting for the new release I think.

[notjosh]

0.1.3 was just released, so I'll rebase & clean up the PR soon....ish. I've got some family in town so it might be a couple of days.

[RazrFalcon]

Sure, no problem.

[notjosh]

Okie doke, tests are green locally, so this should now be ready to review.

[notjosh]

error: package image-webp v0.1.3 cannot be built because it requires rustc 1.67.1 or newer, while the currently active rustc version is 1.65.0

How much of a dealbreaker is this? And/or as image-webp is an optional dependency, anyone that doesn't want to opt into the feature can continue to use < 1.67.1 version, I guess?

[RazrFalcon]

We can bump MSRV no problem. It's set in:

• .github/workflows/main.yml
• README.md

[notjosh]

@RazrFalcon bumped MSRV, can you approve workflow? tyty.

Also, do you want me to bump CHANGELOG.md within the PR, or do you author those (for consistency etc)?

[RazrFalcon]

All good, thanks.