Make the next version emscripten 4.0.0!

[sbc100]

We have a whole bunch of significant change in the next release:

• 3 new wasm features enabled by default
• Use of async/await internally and in MODULARIZE mode
• LLVM libraries updated for v19.1
• Lots of old polyfills finally removed

Also, 74 revisions the 3.1 release is gettting pretty long in the tooth.

Plus it will be the first release of the new year!

[sbc100]

The wider discussion of the future of versioning is still up in the air: #19053, but that shouldn't causes us version paralysis in the meantime.

[kripken]

Sounds good!

Let's give it a longer than usual time to bake before the release, though, given all these changes. Anyhow, we can think about that next year...

[msqr1]

Finally...! After staying at 3.x.x for like 5 years.

[cclauss]

Congrats on reaching v4. Should the testing versions be upgraded, or are they kept back on purpose?

.circleci/config.yml

executors:
  linux-node:
    docker:
      - image: cimg/node:18.20.3
  linux-python:
    docker:
      - image: cimg/python:3.10.7
  bionic:
    docker:
      - image: emscripten/emscripten-ci:focal

[sbc100]

Congrats on reaching v4. Should the testing versions be upgraded, or are they kept back on purpose?

.circleci/config.yml

executors:
  linux-node:
    docker:
      - image: cimg/node:18.20.3
  linux-python:
    docker:
      - image: cimg/python:3.10.7
  bionic:
    docker:
      - image: emscripten/emscripten-ci:focal

I don't think the first two really matter. But the third one we choose deliberately to make sure we test on older versions of linux. If we want to drop support for the version of glibc in Ubuntu/Focal we could update this, but it don't any pressing reason for do that (at least not that I know of).