Merge pull request #14882 from eric-wieser/6103-alias-__getattr__-deprecation

DEP: Deprecate aliases of builtin types in python 3.7+ 

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+Using the aliases of builtin types like ``np.int`` is deprecated
+----------------------------------------------------------------
+
+For a long time, ``np.int`` has been an alias of the builtin ``int``. This is
+repeatedly a cause of confusion for newcomers, and is also simply not useful.
+
+These aliases have been deprecated. The table below shows the full list of
+deprecated aliases, along with their exact meaning. Replacing uses of items in
+the first column with the contents of the second column will work identically
+and silence the deprecation warning.
+
+In many cases, it may have been intended to use the types from the third column.
+Be aware that use of these types may result in subtle but desirable behavior
+changes.
+
+==================  =================================  ==================================================================
+Deprecated name     Identical to                       Possibly intended numpy type
+==================  =================================  ==================================================================
+``numpy.bool``      ``bool``                           `numpy.bool_`
+``numpy.int``       ``int``                            `numpy.int_` (default int dtype), `numpy.cint` (C ``int``)
+``numpy.float``     ``float``                          `numpy.float_`, `numpy.double` (equivalent)
+``numpy.complex``   ``complex``                        `numpy.complex_`, `numpy.cdouble` (equivalent)
+``numpy.object``    ``object``                         `numpy.object_`
+``numpy.str``       ``str``                            `numpy.str_`
+``numpy.long``      ``int`` (``long`` on Python 2)     `numpy.int_` (C ``long``), `numpy.longlong` (largest integer type)
+``numpy.unicode``   ``str`` (``unicode`` on Python 2)  `numpy.unicode_`
+==================  =================================  ==================================================================
+
+Note that for technical reasons these deprecation warnings will only be emitted
+on Python 3.7 and above.