IntervalIndex constructor doesn't use dtype parameter

[jschendel]

Code Sample, a copy-pastable example if possible

The IntervalIndex constructor takes a dtype parameter but doesn't use it (no references to it in the code):

In [2]:  pd.IntervalIndex([pd.Interval(0, 1), pd.Interval(2, 3)], dtype='float64')
Out[2]:
IntervalIndex([(0, 1], (2, 3]]
              closed='right',
              dtype='interval[int64]')

The constructor methods do not support a dtype parameter:

In [3]: pd.IntervalIndex.from_intervals([pd.Interval(0, 1), pd.Interval(2, 3)], dtype='float64')
---------------------------------------------------------------------------
TypeError: from_intervals() got an unexpected keyword argument 'dtype'

In [4]: pd.IntervalIndex.from_arrays([0, 2], [1, 3], dtype='float64')
---------------------------------------------------------------------------
TypeError: from_arrays() got an unexpected keyword argument 'dtype'

In [5]: pd.IntervalIndex.from_breaks([0, 1, 2, 3], dtype='float64')
---------------------------------------------------------------------------
TypeError: from_breaks() got an unexpected keyword argument 'dtype'

In [6]: pd.IntervalIndex.from_tuples([(0, 1), (2, 3)], dtype='float64')
---------------------------------------------------------------------------
TypeError: from_tuples() got an unexpected keyword argument 'dtype'

Expected Output

I'd expect the IntervalIndex constructor and constructor methods to support a dtype parameter, which can be used to override the inferred dtype.