Use tsutils package for utilities

[ajafff]

PR checklist

• Closes: Use a separate package for typeguards and other utilities #2180
• enhancement

What changes did you make?

Use the package tsutils for typeguards and other utility functions.

The idea was to create a separate project which maintains typeguards and AST utilities for everyone, not just tslint and custom rules packages. This way tslint core could remain just a runtime for rules instead of growing to a bulk of utility functions.

[nchen63]

@ajafff thanks!