Drop support of Node v12

[juergba]

Description of the Change

We drop support of Node v12 which will be end-of-life: 2022-04-30

[giltayar]

A bit premature, no? End of April is more than a month and a half away.

There's a lot of test code that we can remove: test code that adds the --experimental-es-modules (or some such), and which we don't need anymore in Node 14. Cleans up things a bit.

I can do that once this lands.

[juergba]

A bit premature, no? End of April is more than a month and a half away.

No, I don't think so, our milestone v10.0.0 has due-date of May-01-2022. There is a lot to do until then as e.g. dropping IE11, we will need those six weeks. The creation date of this PR is not identical with the release date of v10.0.0.

There's a lot of test code that we can remove [...] I can do that once this lands.

Yes, please. And also add .js to the extensionless bin/mocha executable.

[giltayar]

So LGTM