BUG: Wrong Custom Formatters applied when displaying trancated frames
#### Problem description
I am providing custom formatters for specific columns as dict.
If frame is large enough and some columns are truncated - then wrong formatters are applied to the columns.
(In my case that leads to crushes as wrong data type is received by the formatter). 

Please notice, that behavior changes depending on the width of the console window as different columns are displayed.

#### Problem investigation
I have examined the code of my version of panda (1.0.5) and compared with the last version in GitHub - the bug seems to be still there.

The source of the problem starts with this method (`DataFrameFormatter._to_str_columns`), when 
frame is set to truncated ` frame = self.tr_frame` and then `self._format_col(i)` is called with __index of the column in the TRUNCATED frame__:
```python 
    def _to_str_columns(self) -> List[List[str]]:
        """
        Render a DataFrame to a list of columns (as lists of strings).
        """
        # this method is not used by to_html where self.col_space
        # could be a string so safe to cast
        self.col_space = cast(int, self.col_space)

        frame = self.tr_frame
        # may include levels names also

        str_index = self._get_formatted_index(frame)

        if not is_list_like(self.header) and not self.header:
            stringified = []
            for i, c in enumerate(frame):
                fmt_values = self._format_col(i)
```

Then this "truncated" column index is passed to `self._get_formatter`:
```python
    def _format_col(self, i: int) -> List[str]:
        frame = self.tr_frame
        formatter = self._get_formatter(i)   # the problem is HERE? _get_formatter(frame.columns[i]) ?
```
which uses __full frame columns__ to retrieve formatter __using index `i` which corresponds to the columns of the truncated frame__:

```python
           # ...
        else:
            if is_integer(i) and i not in self.columns:
                i = self.columns[i]
            return self.formatters.get(i, None)
```  


<details>

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.6.10.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.0-37-generic
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.0.5
numpy            : 1.18.5
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 20.0.2
setuptools       : 46.0.0.post20200309
Cython           : 0.29.15
pytest           : 5.4.1
hypothesis       : 5.19.3
sphinx           : 2.4.0
blosc            : None
feather          : None
xlsxwriter       : 1.2.8
lxml.etree       : 4.5.0
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.11.1
IPython          : 7.16.1
pandas_datareader: None
bs4              : 4.8.2
bottleneck       : 1.3.2
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.5.0
matplotlib       : 3.2.2
numexpr          : 2.7.1
odfpy            : None
openpyxl         : 3.0.3
pandas_gbq       : None
pyarrow          : None
pytables         : None
pytest           : 5.4.1
pyxlsb           : None
s3fs             : None
scipy            : 1.4.1
sqlalchemy       : 1.3.15
tables           : 3.4.4
tabulate         : 0.8.3
xarray           : 0.15.0
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.2.8
numba            : 0.50.1

</details>
