[SPARK-17981][SPARK-17957][SQL] Fix Incorrect Nullability Setting to False in FilterExec

### What changes were proposed in this pull request?

When `FilterExec` contains `isNotNull`, which could be inferred and pushed down or users specified, we convert the nullability of the involved columns if the top-layer expression is null-intolerant. However, this is not correct, if the top-layer expression is not a leaf expression, it could still tolerate the null when it has null-tolerant child expressions.

For example, `cast(coalesce(a#5, a#15) as double)`. Although `cast` is a null-intolerant expression, but obviously`coalesce` is null-tolerant. Thus, it could eat null.

When the nullability is wrong, we could generate incorrect results in different cases. For example,

``` Scala
    val df1 = Seq((1, 2), (2, 3)).toDF("a", "b")
    val df2 = Seq((2, 5), (3, 4)).toDF("a", "c")
    val joinedDf = df1.join(df2, Seq("a"), "outer").na.fill(0)
    val df3 = Seq((3, 1)).toDF("a", "d")
    joinedDf.join(df3, "a").show
```

The optimized plan is like

```
Project [a#29, b#30, c#31, d#42]
+- Join Inner, (a#29 = a#41)
   :- Project [cast(coalesce(cast(coalesce(a#5, a#15) as double), 0.0) as int) AS a#29, cast(coalesce(cast(b#6 as double), 0.0) as int) AS b#30, cast(coalesce(cast(c#16 as double), 0.0) as int) AS c#31]
   :  +- Filter isnotnull(cast(coalesce(cast(coalesce(a#5, a#15) as double), 0.0) as int))
   :     +- Join FullOuter, (a#5 = a#15)
   :        :- LocalRelation [a#5, b#6]
   :        +- LocalRelation [a#15, c#16]
   +- LocalRelation [a#41, d#42]
```

Without the fix, it returns an empty result. With the fix, it can return a correct answer:

```
+---+---+---+---+
|  a|  b|  c|  d|
+---+---+---+---+
|  3|  0|  4|  1|
+---+---+---+---+
```
### How was this patch tested?

Added test cases to verify the nullability changes in FilterExec. Also added a test case for verifying the reported incorrect result.

Author: gatorsmile <gatorsmile@gmail.com>

Closes #15523 from gatorsmile/nullabilityFilterExec.