🥅 Stricter types in apply()

[alecgibson]

Fixes: ottypes#37

Background

There are some corner cases that arise in the json0 library because -
given an object obj, and an array arr -these statements are both
true in JavaScript:

obj['123'] === obj[123]
arr['123'] === arr[123]

The fact that these statements are true can lead to some unexpected
silent transform() failures:

const op1 = [{p: ['a', '1', 0], si: 'hi'}]
const op2 = [{p: ['a', 1], lm: 0}]

json0.transform(op1, op2, 'left')

Actual result: [{p: ["a", 2, 0], si: "hi"}]
Expected result: [{p: ["a", 0, 0], si: "hi"}]

Solution

In order to prevent this, it's been decided that arrays should always
be indexed by number, and objects should always be indexed by
string.

This change enforces stricter type checks when calling apply(), and
now throws in the following cases:

• When a number is used to key an object property:
  type.apply({'1': 'a'}, [{p:[1], od: 'a'}])
• When a string is used to key an array property:
  type.apply(['a'], [{p:['0'], ld: 'a'}])
• When adding a string to a number:
  type.apply(1, [{p:[], na: 'a}])
• When adding a number to a string:
  type.apply('a', [{p:[], na: 1}])
• When applying a string operation to a non-string:
  type.apply(1, [{p: [0], si: 'a'}])