BUG: mix of int and pd.NA defaults to object dtype
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

---

#### Code Sample, a copy-pastable example

On pandas 1.0.3:

```python
df = pd.DataFrame([7,8,9,pd.NA])
print(df.dtypes) 
# 0    object
# dtype: object
```

#### Problem description

Creating a DataFrame with mixed int and pd.NA defaults to `object` instead of `Int64`

According to @simonjayhawkins in #32931

> since pd.NA is experimental, changing the constructor to default to the best possible dtypes using dtypes supporting pd.NA seems reasonable.

#### Expected Output

```python
pd.DataFrame([7,8,9,pd.NA]).dtypes
# 0    Int64
# dtype: object
```