Separately export (E|T)TSLintRuleOptions, (E|T)SLintRuleSeverity

[JoshuaKGoldberg]

Overview

angular-eslint/angular-eslint#173 (comment): the Angular schematic/integration redeclares TSLintRuleOptions and TSLintRuleSeverity to strongly type the returns of its convertToESLintConfig.

Actual Behavior

These types are declared internally but never exported, so outside folks can't use them.

Expected Behavior

Export them via src/index.ts so Node API users can use them.