Create versioning policy for emscripten

[sbc100]

We should decide if we even plan to use the major or minor version numbers again in emscripten or if we want to simply continue to use patch versions.

If we are going to drop major and minor bumps should we just move so a single number the chrome and firefox do it?

Split out from discussion in #18191 (comment)

[sbc100]

@tlively @juj @kripken @dschuff

Thomas has made that argument that there is quite of benefit in being able to compare two version and get a good idea of how far apart they are in time. For example with Chrome its obvious that v88 is 12 versions older than v100

I've never been a huge fan of semantic versioning myself, so I'd been keen to drop the pretense that that is what we are doing, and admit that there is no such things as a patch-only, risk-free upgrade. I think a single monotonic version is easier to reason about and its also what we have been doing anyway for almost all our emscripten releases to years ( we just happen to have been using the patch level as this number).

[tlively]

I like semantic versioning a lot, but we don't do it and it wouldn't be feasible to start doing it as far as I can tell. I agree that it would be better to avoid giving the impression that we do use semantic versioning. I don't feel strongly about whether we do that via documentation or a change to the version number format.

[curiousdannii]

One option is to simply use the date as the version number.