Relax "no-null-undefined-union" rule.

[nrathi]

PR checklist

• Addresses an existing issue: fixes Relax no-null-undefined-union rule #4617
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

CHANGELOG.md entry:

[rule-change] Relax no-null-undefined-union rule.

[VincentLanglet]

Hi @nrathi

Can you add a test for

type Text = string | null

interface Props {
  title?: Text
}
interface SuperProps {
  title?: Text | number
}

function someFunc(bar?: Text, foo?: Text | number) {}

I don't expect error from the rule, if you do, there should be at least an option to disable these cases.

[nrathi]

@VincentLanglet added, no errors!