add 2 rules in mathematica parser

[asukaminato0721]

References to other Issues or PRs

Brief description of what is fixed or changed

add two rules

ArcTan[x,y] -> atan2(y,x)
Pochhammer[x,y] -> rf(x,y)

Other comments

Release Notes

• parsing
  • Added 2 new rules for mathematica parser.

[sympy-bot]

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• parsing
  • Added 2 new rules for mathematica parser. (#19135 by @wuyudi)

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#### References to other Issues or PRs
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#### Brief description of what is fixed or changed

add two rules

```
ArcTan[x,y] -> atan2(y,x)
Pochhammer[x,y] -> rf(x,y)
```

#### Other comments


#### Release Notes

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on how to write release notes. The bot will check your release notes
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<!-- BEGIN RELEASE NOTES -->
* parsing
  * Added 2 new rules for mathematica parser.
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[codecov]

Codecov Report

Merging #19135 into master will decrease coverage by 0.011%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##            master    #19135       +/-   ##
=============================================
- Coverage   75.762%   75.751%   -0.012%     
=============================================
  Files          650       650               
  Lines       169039    169203      +164     
  Branches     39861     39919       +58     
=============================================
+ Hits        128069    128174      +105     
- Misses       35378     35457       +79     
+ Partials      5592      5572       -20     

[sylee957]

Can you add some tests in test_mathematica.py?

[smitgajjar]

Remove this whole __main__ block from here. Include tests within test_mathematica.py of parsing/tests.