Drop Node.js 12 support, support Node.js 16 & 18

[igoradamenko]

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[igoradamenko]

Originally I was not going to remove ava and nyc. But then after the linter config update I encountered an error, where eslint-import-plugin could not determine whether or not ava was installed.

I spent almost two hours diving into the dep chain, trying to understand what was going on. As a result I've figured out that the resolve package, used by that plugin to, well, resolve the deps, does not support ESM yet:

browserify/resolve#222

“Yet” is 3 years old for now, which probably means that it won't be supported ever.

Buuut, one might ask: “Why only the ava package is the problem here?”

“Good question,” I would answer! Because ava developers decided not to add a main field into their package.json. As they say, everything should work without that field. If it does not work, then it's your problem, not theirs:

avajs/ava#3128

Well, they have their right to develop the package as they want.

Same as we. So I removed ava completely and replaced it with Mocha.