allow switch expressions

[Thomas Grainger]

allow switches of the form:

switch(expr) {
    case (expr): return expr;
    ...
    default: return expr;
}

eg every switch must have a default return expr, every case must have a return expr.
then it's sort of like a match expression.

[Thomas Grainger]

@michalczaplinski, @timbuckley, and @joefraley

To enable FP-switch statements you must set:

"rules": {
    "better/no-switches": 0,
    "better/explicit-return": 0,
    "better/must-return": 2,
    "default-case": 2,
}