ERR: Disallow multi-char quotechar for C engine
Raise `ValueError` or issue `ParserWarning` (as we do with other unsupported features) when a multi-char `quotechar` is passed in, and the C engine is used.

Closes #11592.
## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/15050?src=pr) is 84.76% (diff: 100%)
> Merging [#15050](https://codecov.io/gh/pandas-dev/pandas/pull/15050?src=pr) into [master](https://codecov.io/gh/pandas-dev/pandas/branch/master?src=pr) will increase coverage by **<.01%**

```diff
@@             master     #15050   diff @@
==========================================
  Files           145        145          
  Lines         51146      51151     +5   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43350      43356     +6   
+ Misses         7796       7795     -1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [de09c98...68d69fe](https://codecov.io/gh/pandas-dev/pandas/compare/de09c988dddb519ac59fde1556a6d9d35f43e702...68d69fe9b3c1bdf7715b395d3ac84d9bb25b385d?src=pr) @jreback : Any comments on this PR?  Otherwise, everything is green and ready to go. @sinhrks : Addressed all of your comments, and everything is still green.