Relax TypedRule detection (fix #1637, fix #1522)

[bcherny]

PR checklist

• Addresses an existing issue: Cannot run custom typed rules in the CLI #1637, Custom rule that requires type checking throwing "requires type checking" error #1522
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

What changes did you make?

Relax TypedRule detection:

• TypedRule exists to notify the consumer that they must implement the applyWithProgram method.
• Checking instanceof is fragile, as is checking constructor.name.
• Checking isTypedRule makes the API bulkier, though it is more explicit, which is good. My rationale is if the consumer defined applyWithProgram, then the intention is to make the rule a typed rule, so an additional flag is probably not necessary.

[palantirtech]

Thanks for your interest in palantir/tslint, @bcherny! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[adidahiya]

nice, I was just about to comment suggesting that you implement this with a type guard :)

[bcherny]

Yeah, that assert was ugly :)