Node18 compatibility and more

[stronk7]

We need to support Node 18 from the CI tools (see MDL-75012). So
this commit provides that, basically.

The main difference is that the npm bin command is not available
anymore, and that's what we used both for:

1. Search if a given binary has been installed (say, grunt-cli...)
2. Launch a number of binaries (grunt, eslint, gherkin-lint....)

So here we are geting rid of all those uses, changing them by:

1. npm list to verify if a package is already installed.
2. npx to launch the binaries.

Also, we have removed some very-old conditional blocks in the code, that
were providing compatibility with very, very old Moodle branches, before
we used grunt and friends.

Finally, we are now installing stylelint-checkstyle-formatter if
it's detected that core has not installed it. After all, it's a CI
dependency, not a core one, so maybe the more correct thing is to
delegate its installation to the CI / testing tools.

And, basically, that is. I've tested it with both Node 16 (current
master) and Node 18 (MDL-75012) and seems to be working ok.

Let's see if it finally pass testing. It's passing locally but have got some non-sense results in the last execution @ Travis... 🤞

[andrewnicols]

These changes look good to me.

We should decide when we want to stop supporting v14 of node, but it won't be for a while - we only switched away from it 12 months ago:

commit ef74e31086bc78ab84a6fbb0fbbb408d855e5bf4
Author: Andrew Nicols <andrew@nicols.co.uk>
Date:   Fri Feb 18 08:07:49 2022 +0800

    MDL-73915 js: Switch to nodejs lts/gallium

So I think this is good to land when tests finish.

[stronk7]

We are green now, hence merging, thanks for the review @andrewnicols !