[GSoC] Functions: Adds cdir parameter to handle series expansions on branch cuts

[sachin-4099]

Fixes: #7216
Fixes: #19586

Brief description of what is fixed or changed

Adds cdir parameter to handle series expansions on branch cuts.
cdir stands for complex direction, and indicates the direction from which the expansion needs to be evaluated.

Other Comments

Regression Tests have been added.

Release Notes

• functions
  • Adds cdir parameter to handle series expansions on branch cuts

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• functions
  • Adds cdir parameter to handle series expansions on branch cuts (#19555 by @sachin-4099)

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Fixes: #7216
Fixes: #19586 

#### Brief description of what is fixed or changed

Adds `cdir` parameter to handle `series expansions` on `branch cuts`.
`cdir` stands for `complex direction`, and indicates the direction from which the expansion needs to be evaluated.



#### Other Comments
Regression Tests have been added.


#### Release Notes


<!-- BEGIN RELEASE NOTES -->
* functions
  * Adds `cdir` parameter to handle `series expansions` on `branch cuts`
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[codecov]

Codecov Report

Merging #19555 into master will increase coverage by 8.066%.
The diff coverage is 80.709%.

@@              Coverage Diff              @@
##            master    #19555       +/-   ##
=============================================
+ Coverage   67.624%   75.691%   +8.066%     
=============================================
  Files          654       656        +2     
  Lines       169939    170543      +604     
  Branches     40065     40235      +170     
=============================================
+ Hits        114921    129086    +14165     
+ Misses       49388     35798    -13590     
- Partials      5630      5659       +29     

[jksuom]

Thanks, I think this is ready to go.