fix: upgrade babel from 6 to 7

[armano2]

Description

Doing this update was not trivial task, a lot of dependencies relied on older version of packages and i upgraded only what i had to.

Changes

• migrate from babel 6 to babel 7
• upgrade ava 0.x to 2.4 - relies heavily on babel
• upgrade all require/exports. to import/export
• drop babel-polyfill and replace it with direct reference to corejs@3
corejs@2 is no longer maintained

Motivation and Context

corejs@2 is no longer maintained, babel@6 is outdated

Usage examples

No changes

How Has This Been Tested?

Unit tests

Types of changes

• Dependencies
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I updated tests to run with new versions of ava

[armano2]

if its ok, in follow up PR i'm planning to drop proxyrequire (this package is no longer needed).
and upgrading all tests from ava to jest

[byCedric]

This is some solid work, thanks ❤️ I'll review it asap, it's kind of big 😄 Can definitely help us move the TypeScript refactor forward again! @marionebl @escapedcat What do you think?

[byCedric]

Looks good to me! ❤️ What do you think @marionebl @escapedcat?

[escapedcat]

Great job! Thanks a bunch!

[byCedric]

@armano2 Thanks for all the effort you put into this PR, I'm going to merge and continue from there with the TypeScript refactor ❤️ (cc @marionebl, @escapedcat)

[stieben]

It would be awesome to see this change published to npm, as the current v8.3.5 causes a warning regarding corejs@2 being no longer maintained.

(As of now, master is 99 commits ahead of v8.3.5.)