Add whitespace rule for ExportDeclaration

[devmattrick]

PR checklist

• Addresses an existing issue: fixes Missing whitespace around export statement with "check-module" argument #4014
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Adds a case to handle ExportDeclaration, to properly lint and fix statements such as:

export { A, B };

CHANGELOG.md entry:

[bugfix] Lint export statements with whitespace rule

[JoshuaKGoldberg]

Looks great, thanks!

Although TSLint is moving away from whitespace rules, the presense of an auto-fixer and the issue already having been marked as Status: Accepting PRs makes this seem reasonable.