ESLint for TypeScript

[azu]

Meta issue for typescript-eslint integration.

Enable lint for TypeScript code.

Separated steps and Separated Tasks.

• [ ] Introduce ESLint for TypeScript #684 by @zweimach
• [ ] Setup configuration
  • [ ] We may need to suppress or change severity for some rules
  • @typescript-eslint/no-unsafe-assignment
  • @typescript-eslint/no-unsafe-member-access
  • Should we use same config between src and test?
• [ ] Fix code to pass linting
• [ ] Enable ESLint for TypeScript in CI
  • https://github.com/textlint/textlint/blob/6fff8016b1f26fd34e650d89827c52ae7b2de4f0/package.json#L9-L10

Welcome to contribute this task!

[azu]

Fix code to pass linting

Maybe, This task require a lots of people power. We welcome to contribute.