Drop Node 14 support

[amcaplan]

WHY are these changes introduced?

Node 14 has long been EoL. We now warn if it's used, our docs say you need 18+, and in practice it's now used by < 0.5% of users on a recent CLI version.

Time for Node 14 to go!

WHAT is this pull request doing?

Specifies a requirement for Node 16+ in all package.jsons that previously stated 14 was ok.

How to test your changes?

N/A

Measuring impact

How do we know this change was effective? Please choose one:

• n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• Existing analytics will cater for this addition
• PR includes analytics changes to measure impact

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've made sure that any changes to dev or deploy have been reflected in the internal flowchart.

[github-actions]

Thanks for your contribution!

Depending on what you are working on, you may want to request a review from a Shopify team:

• Themes: @shopify/advanced-edits
• UI extensions: @shopify/ui-extensions-cli
  • Checkout UI extensions: @shopify/checkout-ui-extensions-api-stewardship
• Hydrogen: @shopify/hydrogen
• Other: @shopify/cli-foundations

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	73.08% (-0.01% 🔻)	6256/8561
🟡	Branches	70.71% (-0.02% 🔻)	3044/4305
🟡	Functions	71.75%	1585/2209
🟡	Lines	74.22% (-0.01% 🔻)	5941/8005

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟢	... / ConcurrentOutput.tsx	97.62% (-2.38% 🔻)	75% (-8.33% 🔻)	100%	97.44% (-2.56% 🔻)

Test suite run success

1494 tests passing in 670 suites.

Report generated by 🧪jest coverage report action from 5a17889