Support Nullish Coalescing in Rules

[bradzacher]

Spinning off of #1033

Rules that need to have support added for optional chaining.
This list was based on a simple grep for LogicalExpression, I haven't validated anything beyond that. There are probably extra rules that could do with support as well that don't check LogicalExpression.

• no-extra-parens (issue: [no-extra-parens] Incorrect rule flagging when using '??' #1155)
  • Same as for optional chaining (Support Optional Chaining in Rules #1051) - this one will be a huge pain, and I believe it will involve us duplicating the base rule. The logic is relatively complex, so this is a non-trivial task.
• no-misused-promises this is already
• no-unnecessary-condition (feat(eslint-plugin): [no-unnec-cond] support nullish coalescing #1148)
• strict-boolean-expressions (fix(eslint-plugin): [strict-bool-expr] allow nullish coalescing #1275)
• unbound-method (fix(eslint-plugin): [unbound-method] handling of logical expr #1440)

[bradzacher]

This should now all be supported by ESLint core.