Filter env vars to always be valid for ESBuild

[amcaplan]

Nothing beginning with a number!

More details at https://github.com/evanw/esbuild/blob/44e746965d783646f97daf3d0617ff816727e7fb/internal/js_ast/js_ident.go#L9-L25

WHY are these changes introduced?

Fixes #3649

ESBuild has very strict rules about which ENV variables are allowed. One of the rules is no numeric characters at the beginning.

WHAT is this pull request doing?

Disallows numeric characters at the start of the ENV variable name.

How to test your changes?

For an app with an extension:

$ env '1VAR=value' p shopify app dev --path /path/to/your/app/with/ui/extensions

This should fail on main and succeed on this branch.

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	72.02% (+0.01% 🔼)	6768/9398
🟡	Branches	69.1% (+0.02% 🔼)	3316/4799
🟡	Functions	70.82%	1806/2550
🟡	Lines	73.17% (+0.01% 🔼)	6382/8722

Test suite run success

1620 tests passing in 755 suites.

Report generated by 🧪jest coverage report action from 27ae7f3