Assign multiple variables from a hash

In PUP-2894, the ability to assign multiple variables from an array was added. When using this to refactor typical code it became apparent that this is useful when there are only a few values to assign, or where there is a simple 1:1 map in a single place. Real world code typically need this feature to assign 10 (typical) but up to as many as 30-50 variables - with very high redundancy.

As it is difficult to writes arrays that merge, it is of great value to be able to assign multiple variables based on a hash.

[$a, $b] = {a => 10, b => 20}

The rules are:

• for each entry in the array, there must be a corresponding key in the hash
• the hash key must be based on the String variable name(s)
• if the hash does not have a corresponding key the operation fails
• there may be additional key/values in the hash
• if an element in the LHS array is an Array with multiple variables, the corresponding key in the hash must be an Array with the String names in the same order e.g.

  [[$a, $b], $c] = {[a,b] => {a => 10, b => 20 }, c => 30 }