Count anagram pairs

Given a list of lowercase words, count how many unordered index pairs (i, j) with i < j hold words that are anagrams of each other, identical letters with identical multiplicities, such as "tab" and "bat". Identical words are trivially anagrams, so repeated words form pairs too. For example, ["tab", "bat", "cat", "act", "atb"] has the anagram family {tab, bat, atb} contributing three pairs and {cat, act} contributing one, for an answer of 4. Comparing all pairs directly is O(n^2), group first instead.