Add UseStringMethodCharOverloadWithSingleCharacters analyzer and fixer

[mrahhal]

Resolves dotnet/runtime#78392

cc @tarekgh @Youssef1313 @stephentoub

[codecov]

Codecov Report

Merging #6799 (f159d4c) into main (b3274a6) will increase coverage by 0.00%.
Report is 9 commits behind head on main.
The diff coverage is 95.27%.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #6799    +/-   ##
========================================
  Coverage   96.34%   96.34%            
========================================
  Files        1386     1394     +8     
  Lines      326229   327150   +921     
  Branches    10729    10768    +39     
========================================
+ Hits       314296   315206   +910     
- Misses       9225     9230     +5     
- Partials     2708     2714     +6     

[tarekgh]

@mrahhal let's know when you finish all coding so we can review it in one shot. Thanks!

[mrahhal]

@tarekgh Resolved all the pending conversations (except for the severity thing). Ready for another round of review.

[tarekgh]

@Youssef1313 @buyaa-n it looks you are already reviewing the PR. Thanks for that. I finished reviewing and LGTM. Please let me know if you have any more comments here.

@stephentoub do you want to take a quick look?

CC @carlossanlop as you have added some analyzer and may have any comment.

[tarekgh]

Thanks @mrahhal for helping implementing it.

Are you interested in playing more with the analyzers? dotnet/runtime#78406 is a good one you may consider if you are interested and if @Youssef1313 not doing it :-)

[mrahhal]

Thanks for the reviews. Yes I'm planning to look at more from the table.

Working on the docs PR for this, will post here.

[mrahhal]

Docs PR: dotnet/docs#36417