make node-addon-api examples context-sensistive

[gabrielschulhof]

This removes global static references from the examples, so that they
might work with worker threads.

[gabrielschulhof]

Looks like Travis doesn't yet have a version of Node.js 12.x that ships with N-API 6.

[gengjiawen]

Looks like Travis doesn't yet have a version of Node.js 12.x that ships with N-API 6.

Maybe limit version like this

node-addon-examples/thread_safe_function_round_trip/napi/package.json

Lines 10 to 13 in b024ee9

	"engines": {
	"node": ">= 10.6.0"
	},
	"scripts": {

Also github action looks like not using latest Node.js 12 yet

[gengjiawen]

I give it more test, should '~10 >=10.20 || >=12.17 ' work.

const semver = require('semver')
const assert = require('assert').strict

const rule = '~10 >=10.20 || >=12.17 '
assert.equal(false, semver.satisfies('10.19.0', rule))
assert.ok(semver.satisfies('10.20.0', rule))
assert.equal(false, semver.satisfies('12.16.0', rule))
assert.ok(semver.satisfies('12.19.0', rule))

[gabrielschulhof]

@nodejs/n-api it looks like it's not Travis that has old versions of Node.js but GitHub actions. Thus, with the "engines" change proposed by @gengjiawen the examples are actually only run on Travis so we have some testing there.

[gabrielschulhof]

It looks like github by default doesn't grab the latest available version of Node.js if one specifies "10.x" or "12.x", but will grab the latest version if one specifies it exactly (I used "10.21.0" and "12.18.0").

[gabrielschulhof]

So, now the examples are run on both Travis and GitHub actions.