BUG: 35977 Adding regex support for ExtensionBlock replace method
- [x] closes #35977 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Overrides replace method to add support of regex in ExtensionBlock . If input to_replace is a regex we convert data type of block to Object and calls object replace method which supports regex otherwise we call replace method of super class Block.

```ipython
In [2]: b.replace(r'^\s*$', pd.NA, regex=True, inplace=True)
   ...: print(b)
   a     b
0  a     d
1  b  <NA>
2  c  <NA>

In [3]: b.replace(r'^\s*$', pd.NA, regex=True, inplace=False)
Out[3]: 
   a     b
0  a     d
1  b  <NA>
2  c  <NA>


```
pls merge master as we just merged a change in how replace works in internals. @jreback synced with upstream master also verified that this bug is still present in upstream master @cgangwar11

Conflicting files
pandas/tests/arrays/categorical/test_replace.py Also will need to merge master Hello @cgangwar11! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-11-15 07:14:13 UTC This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. closing as stale. if you want to continue, pls ping and can re-open.