BUG: Cannot convert from `object` numeric strings to Float64Dtype
#### Code Sample, a copy-pastable example

```python
import pandas as pd

series = pd.Series(['1', '2', '3', '4'], dtype='object')
series.astype(pd.Float64Dtype())
```

the above produces a `TypeError: object cannot be converted to a FloatingDtype`:
<details>


```python-traceback
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-20-a9dee24fff9e> in <module>
     15 assert series.astype('float64').dtype == 'float64'
     16 # TypeError: object cannot be converted to a FloatingDtype - same for DataFrames
---> 17 series.astype(pd.Float64Dtype())
     18 

~/.pyenv/versions/3.8.2/envs/woodwork/lib/python3.8/site-packages/pandas/core/generic.py in astype(self, dtype, copy, errors)
   5875         else:
   5876             # else, only a single dtype is given
-> 5877             new_data = self._mgr.astype(dtype=dtype, copy=copy, errors=errors)
   5878             return self._constructor(new_data).__finalize__(self, method="astype")
   5879 

~/.pyenv/versions/3.8.2/envs/woodwork/lib/python3.8/site-packages/pandas/core/internals/managers.py in astype(self, dtype, copy, errors)
    629         self, dtype, copy: bool = False, errors: str = "raise"
    630     ) -> "BlockManager":
--> 631         return self.apply("astype", dtype=dtype, copy=copy, errors=errors)
    632 
    633     def convert(

~/.pyenv/versions/3.8.2/envs/woodwork/lib/python3.8/site-packages/pandas/core/internals/managers.py in apply(self, f, align_keys, ignore_failures, **kwargs)
    425                     applied = b.apply(f, **kwargs)
    426                 else:
--> 427                     applied = getattr(b, f)(**kwargs)
    428             except (TypeError, NotImplementedError):
    429                 if not ignore_failures:

~/.pyenv/versions/3.8.2/envs/woodwork/lib/python3.8/site-packages/pandas/core/internals/blocks.py in astype(self, dtype, copy, errors)
    671             vals1d = values.ravel()
    672             try:
--> 673                 values = astype_nansafe(vals1d, dtype, copy=True)
    674             except (ValueError, TypeError):
    675                 # e.g. astype_nansafe can fail on object-dtype of strings

~/.pyenv/versions/3.8.2/envs/woodwork/lib/python3.8/site-packages/pandas/core/dtypes/cast.py in astype_nansafe(arr, dtype, copy, skipna)
   1017     # dispatch on extension dtype if needed
   1018     if is_extension_array_dtype(dtype):
-> 1019         return dtype.construct_array_type()._from_sequence(arr, dtype=dtype, copy=copy)
   1020 
   1021     if not isinstance(dtype, np.dtype):

~/.pyenv/versions/3.8.2/envs/woodwork/lib/python3.8/site-packages/pandas/core/arrays/floating.py in _from_sequence(cls, scalars, dtype, copy)
    278         cls, scalars, *, dtype=None, copy: bool = False
    279     ) -> "FloatingArray":
--> 280         values, mask = coerce_to_array(scalars, dtype=dtype, copy=copy)
    281         return FloatingArray(values, mask)
    282 

~/.pyenv/versions/3.8.2/envs/woodwork/lib/python3.8/site-packages/pandas/core/arrays/floating.py in coerce_to_array(values, dtype, mask, copy)
    160             "mixed-integer-float",
    161         ]:
--> 162             raise TypeError(f"{values.dtype} cannot be converted to a FloatingDtype")
    163 
    164     elif is_bool_dtype(values) and is_float_dtype(dtype):

TypeError: object cannot be converted to a FloatingDtype

```

</details>

#### Problem description

With `float64`, this conversion works, and as the series' dtype would get inferred as `object` even if no dtype was specified, it is unexpected to me that we would not be able to convert to the `Float64Dtype` from that. 

#### Expected Output

```python
pd.Series([1.0, 2.0, 3.0, 4.0], dtype=Float64Dtype) 
```

#### Output of ``pd.show_versions()``


<details>

INSTALLED VERSIONS
------------------
commit           : f2c8480af2f25efdbd803218b9d87980f416563e
python           : 3.8.2.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 19.6.0
Version          : Darwin Kernel Version 19.6.0: Sun Jul  5 00:43:10 PDT 2020; root:xnu-6153.141.1~9/RELEASE_X86_64
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.2.3
numpy            : 1.19.5
pytz             : 2021.1
dateutil         : 2.8.1
pip              : 21.0.1
setuptools       : 41.2.0
Cython           : None
pytest           : 6.0.1
hypothesis       : None
sphinx           : 3.2.1
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.3
IPython          : 7.18.1
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : 0.8.7
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 3.0.0
pyxlsb           : None
s3fs             : None
scipy            : 1.6.2
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None
