[BE]: Enable readability-simplify-subscript-expr clang-tidy check (py…

…torch#116356)

[BE]: enable clang-tidy check for readability-simplify-subscript-expr which looks for unnecessarily complex subscripting of the underlying data array of STL types.
Pull Request resolved: pytorch#116356
Approved by: https://github.com/lezcano

.clang-tidy

@@ -56,6 +56,7 @@ readability-delete-null-pointer,
 readability-duplicate-include
 readability-misplaced-array-index,
 readability-redundant-smartptr-get,
+readability-simplify-subscript-expr,
 readability-string-compare,
 '
 HeaderFilterRegex: '^(aten/|c10/|torch/).*$'