1002. Find Common Characters 
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Problem
Given a string array words, return an array of all characters that show up in all strings within the words (including duplicates). You may return the answer in any order.
Example 1:
Input: words = ["bella","label","roller"] Output: ["e","l","l"]
Example 2:
Input: words = ["cool","lock","cook"] Output: ["c","o"]
Constraints:
1 <= words.length <= 1001 <= words[i].length <= 100words[i]consists of lowercase English letters.