Given a non-null String containing words separated by the "_" character, write a method wordCount that
return a Map<String, Integer> containing the number of times that each part appears in the String.
So, for example, given the String "Xyz_Chuchu_Chuchu_Xyz_Ferdie", you would return a map with three mappings:
"Xyz" to 2, "Chuchu" to 2, and "Ferdie" to 1.
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