Improve arrow function support

[mgfalzon]

Motivation

This change decreases the JS output for Confluence by 366kb. For large applications the bytes add up quick!

Other smaller optimizations to consider:

• Replacing other helper function calls with arrow function
• Changing parcelRequire.register to parcelRequire.r
• Reducing the size of parcelRequireName, the current definition for confluence is parcelRequired477 which shows up in 3721 files in Conflunece. Reducing it to rd477 would save 44kb.

Changes

• Use arrow functions in parcelRegister calls
• Reduce calls to this.bundle.env.supports('arrow-functions', true);

Checklist

• Existing or new tests cover this change
• There is a changeset for this change, or one is not required

[changeset-bot]

🦋 Changeset detected

Latest commit: f6ee6cb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

Name	Type
@atlaspack/packager-js	Minor
@atlaspack/config-default	Patch
@atlaspack/config-repl	Patch
@atlaspack/config-webextension	Patch
@atlaspack/cli	Patch
@atlaspack/register	Patch
@atlaspack/test-utils	Patch

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[yamadapc]

LGTM but you should feature-flag it

[marcins]

The factory function is called with this bound to module.exports.. can we guarantee that none of the code we have assumes that this is equal to exports for it to function? (Less so "our" code, more third party deps in node_modules that may be built in weird and wonderful ways..)

I have some vague recollection we ran into one third party dep that broke due to this in Jira - because if I remember correctly we did have this change in PR at some point in the past.