Add, remove and sort Map entries

Write a function applyChanges(initial, toAdd, toRemove) that changes a map in three steps and returns its entries sorted by key.

• initial and toAdd are arrays of pairs [key, value]. The key is a string, the value is a number. Keys inside initial are unique, keys inside toAdd are unique too.
• toRemove is an array of keys.
• Step 1: create a Map from initial.
• Step 2: add every pair of toAdd. If the key is already in the map, it gets the new value.
• Step 3: delete every key of toRemove from the map. A key that is not in the map is ignored.
• Return a new array of [key, value] pairs, sorted by key. Compare keys as plain strings, the way sort() with no compare function orders strings: capital letters come before small letters, and a key comes before a longer key that starts with it. So 'Banana' comes before 'apple', and 'item' comes before 'item 2'.
• Keys can contain capital letters and spaces. Any of the three arrays can be empty. If the map is empty at the end, return [].