webp support available in php 7.1+

[sbulen]

Description

Add webp support.

Additional information/references

A support topic mentioned there was an issue logged - I don't think there is one, so just adding it.
https://www.simplemachines.org/community/index.php?topic=574576.msg4083346#msg4083346

@albertlast had a PR out there at one point:
#6271

[albertlast]

my pr got decllinded, so the problem is not real?

[MissAllSunday]

The already logged issue: #6271 a PR is considered an issue.

So far no one has come up with a valid reason as to why we need to add it other than "because google says so."

Post hard data on its usage across the web.

[albertlast]

when google with chrome, how got the major usage of browsers, say that webp is the next thing.
than had you show us why they lie.
give us hard data.

[MissAllSunday]

I'm not the one making the proposal and I'm neither against nor in favor of it.

[sbulen]

Current stats indicate 1.2% & growing.

Source:
https://w3techs.com/technologies/details/im-webp

I view it more an example of keeping current with php, as getimagesize now returns it as a valid image type.

[sbulen]

The code would need to account for php 7.1 vs prior. The constant isn't defined in 7.0.

Lots of undefined constant issues out there due to improper implementation.

[sbulen]

This is a good idea for a future release, but should not hold up RC4 or final.