add type promotion logic for eager between tensor and tensor

[zxcd]

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Description

Card-64022
add type promotion logic for eager between tensor and tensor.

stage 1 will only support float in "+ - *, where" API.
Example like:

>>> a = paddle.randn((2,3), dtype='float32')
>>> b = paddle.randn((2,3), dtype='float64')
>>> out = a + b

# Before, dtype of out would be same to the former one, i.e. a
>>> out.dtype
<VarType.FP32: 5>

# Now, dtype will be promote to float64
>>> out
<VarType.FP64: 6>

[paddle-bot]

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[jeff41404]

LGTM