[SPARK-21394][SPARK-21432][PYTHON] Reviving callable object/partial function...

[SPARK-21394][SPARK-21432][PYTHON] Reviving callable object/partial function support in UDF in PySpark

## What changes were proposed in this pull request?

This PR proposes to avoid `__name__` in the tuple naming the attributes assigned directly from the wrapped function to the wrapper function, and use `self._name` (`func.__name__` or `obj.__class__.name__`).

After SPARK-19161, we happened to break callable objects as UDFs in Python as below:

```python
from pyspark.sql import functions

class F(object):
    def __call__(self, x):
        return x

foo = F()
udf = functions.udf(foo)
```

```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../spark/python/pyspark/sql/functions.py", line 2142, in udf
    return _udf(f=f, returnType=returnType)
  File ".../spark/python/pyspark/sql/functions.py", line 2133, in _udf
    return udf_obj._wrapped()
  File ".../spark/python/pyspark/sql/functions.py", line 2090, in _wrapped
    functools.wraps(self.func)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/functools.py", line 33, in update_wrapper
    setattr(wrapper, attr, getattr(wrapped, attr))
AttributeError: F instance has no attribute '__name__'
```

This worked in Spark 2.1:

```python
from pyspark.sql import functions

class F(object):
    def __call__(self, x):
        return x

foo = F()
udf = functions.udf(foo)
spark.range(1).select(udf("id")).show()
```

```
+-----+
|F(id)|
+-----+
|    0|
+-----+
```

**After**

```python
from pyspark.sql import functions

class F(object):
    def __call__(self, x):
        return x

foo = F()
udf = functions.udf(foo)
spark.range(1).select(udf("id")).show()
```

```
+-----+
|F(id)|
+-----+
|    0|
+-----+
```

_In addition, we also happened to break partial functions as below_:

```python
from pyspark.sql import functions
from functools import partial

partial_func = partial(lambda x: x, x=1)
udf = functions.udf(partial_func)
```

```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../spark/python/pyspark/sql/functions.py", line 2154, in udf
    return _udf(f=f, returnType=returnType)
  File ".../spark/python/pyspark/sql/functions.py", line 2145, in _udf
    return udf_obj._wrapped()
  File ".../spark/python/pyspark/sql/functions.py", line 2099, in _wrapped
    functools.wraps(self.func, assigned=assignments)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/functools.py", line 33, in update_wrapper
    setattr(wrapper, attr, getattr(wrapped, attr))
AttributeError: 'functools.partial' object has no attribute '__module__'
```

This worked in Spark 2.1:

```python
from pyspark.sql import functions
from functools import partial

partial_func = partial(lambda x: x, x=1)
udf = functions.udf(partial_func)
spark.range(1).select(udf()).show()
```

```
+---------+
|partial()|
+---------+
|        1|
+---------+
```

**After**

```python
from pyspark.sql import functions
from functools import partial

partial_func = partial(lambda x: x, x=1)
udf = functions.udf(partial_func)
spark.range(1).select(udf()).show()
```

```
+---------+
|partial()|
+---------+
|        1|
+---------+
```

## How was this patch tested?

Unit tests in `python/pyspark/sql/tests.py` and manual tests.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #18615 from HyukjinKwon/callable-object.