[Python] pa.array raises for mixed scalar types (float16 + int)

[asfimport]

pa.array raises with mixed scalars for np.float16 and a numpy int: 

In [1]: import numpy as np 
 ...: import pyarrow as pa 
 ...: pa.array([np.float16(1.5), np.int64(5)]) 
---------------------------------------------------------------------------
ArrowInvalid Traceback (most recent call last)
<ipython-input-2-b1e9d890f325> in <module>
 1 import numpy as np
 2 import pyarrow as pa
----> 3 pa.array([np.float16(1.5), np.int64(5)])
~/git_repo/arrow/python/pyarrow/array.pxi in pyarrow.lib.array()
 269 else:
 270 # ConvertPySequence does strict conversion if type is explicitly passed
--> 271 return _sequence_to_array(obj, mask, size, type, pool, c_from_pandas)
 272 
 273
~/git_repo/arrow/python/pyarrow/array.pxi in pyarrow.lib._sequence_to_array()
 38 
 39 with nogil:
---> 40 check_status(ConvertPySequence(sequence, mask, options, &out))
 41 
 42 if out.get().num_chunks() == 1:
~/git_repo/arrow/python/pyarrow/error.pxi in pyarrow.lib.check_status()
 82 
 83 if status.IsInvalid():
---> 84 raise ArrowInvalid(message)
 85 elif status.IsIOError():
 86 # Note: OSError constructor is
ArrowInvalid: Cannot mix NumPy dtypes float16 and int64 

On master I get the same behaviour with all numpy ints (signed and unsigned)

Reporter: Andrew Wieteska / @arw2019

_{Note: This issue was originally created as ARROW-9817. Please see the migration documentation for further details.}

[pitrou]

This bug can still be reproduced. @raulcd @AlenkaF