Add 4096 image size and jpeg format that discord supports

[Roki100]

Please describe the changes this PR makes and why it should be merged:
Discord also allows to open avatars/icons in ?size=4096 and discord.js was supporting upto 2048 so im opening this pr, also format .jpeg is a thing and it was not listed in d.js

Status

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Semantic versioning classification:

• This PR changes the library's interface (methods or parameters added)
  • This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
• This PR only includes non-code changes, like changes to documentation, README, etc.

[didinele]

LGTM

[vladfrangu]

Please update the JSDocs accordingly as well

https://github.com/discordjs/discord.js/blob/master/src/util/Constants.js#L110

[Jyguy]

Typings also need to be updated:

AllowedImageFormat
ImageSize

While you're at it, ImageExt should be removed completely as it is a duplicate of AllowedImageFormat. (changes in lines 2546 and 2551)

[SpaceEEC]

The size of 4096 seems to be undocumented currently, see the Discord Developer Documentation - Reference - Image Formatting:

Image size can be any power of two between 16 and 2048.

This could be Discord not documenting a new feature, or something they are experimenting with, that may go away again.

[Roki100]

The size of 4096 seems to be undocumented currently, see the Discord Developer Documentation - Reference - Image Formatting:

Image size can be any power of two between 16 and 2048.

This could be Discord not documenting a new feature, or something they are experimenting with, that may go away again.

as always in discord docs, it was not updated as many things in the docs, after i told my friend that 4096 is valid he decided to make a pr and it got almost instantly merged (see: #1501)
(4096 is a thing for more than a year now)

[SpaceEEC]

As usual.
I didn't see the PR over there yet.
We are good to go then!