Fix some issues of initializing Poly from domain element

[sylee957]

References to other Issues or PRs

Brief description of what is fixed or changed

This resolves two issues with Poly initialized with arguments of DomainElement.

One problem is that the constructor assumes PolyElement as an iterable and initializes with unpacked form even if the PolyElement has different generators.

>>> from sympy import *
>>> x, y = symbols('x y')
>>> dom = ZZ.poly_ring(x)
>>> Poly(dom(x+2), y, domain=dom)
# Should be Poly(x + 2, y, domain='ZZ[x]') 
# but it gives Poly(y + 2, y, domain='ZZ[x]')

The other problem is that FracFieldElement is not working because of sympify error.

>>> from sympy import *
>>> x, y = symbols('x y')
>>> dom = ZZ.frac_field(x)
>>> Poly(dom(x+2), y, domain=dom)
# Should be Poly(x + 2, y, domain='ZZ(x)')

Other comments

Release Notes

• polys
  • Fixed Poly initialized with PolyElement mutating the generator of the coefficient in the form of polynomial.
    (e.g. Poly(ZZ[x](x+1), y, domain=ZZ[x]) becomes Poly(y+1, y, domain=ZZ[x]))
  • Fixed Poly initialized with FracElement raising SympifyError.
    (e.g. dom = ZZ.frac_field(x); Poly(dom(x+2), y, domain=dom))

[sympy-bot]

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Here is what the release notes will look like:

• polys

  • Fixed Poly initialized with PolyElement mutating the generator of the coefficient in the form of polynomial.
    (e.g. Poly(ZZ[x](x+1), y, domain=ZZ[x]) becomes Poly(y+1, y, domain=ZZ[x])) (#19659 by @sylee957)

  • Fixed Poly initialized with FracElement raising SympifyError.
    (e.g. dom = ZZ.frac_field(x); Poly(dom(x+2), y, domain=dom)) (#19659 by @sylee957)

This will be added to https://github.com/sympy/sympy/wiki/Release-Notes-for-1.7.

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

This resolves two issues with Poly initialized with arguments of DomainElement.

One problem is that the constructor assumes `PolyElement` as an iterable and initializes with unpacked form even if the `PolyElement` has different generators.
```
>>> from sympy import *
>>> x, y = symbols('x y')
>>> dom = ZZ.poly_ring(x)
>>> Poly(dom(x+2), y, domain=dom)
# Should be Poly(x + 2, y, domain='ZZ[x]') 
# but it gives Poly(y + 2, y, domain='ZZ[x]')
```

The other problem is that FracFieldElement is not working because of sympify error.
```
>>> from sympy import *
>>> x, y = symbols('x y')
>>> dom = ZZ.frac_field(x)
>>> Poly(dom(x+2), y, domain=dom)
# Should be Poly(x + 2, y, domain='ZZ(x)')
```

#### Other comments


#### Release Notes

<!-- Write the release notes for this release below. See
https://github.com/sympy/sympy/wiki/Writing-Release-Notes for more information
on how to write release notes. The bot will check your release notes
automatically to see if they are formatted correctly. -->

<!-- BEGIN RELEASE NOTES -->
- polys
  - Fixed `Poly` initialized with `PolyElement` mutating the generator of the coefficient in the form of polynomial. 
  (e.g. `Poly(ZZ[x](x+1), y, domain=ZZ[x])` becomes `Poly(y+1, y, domain=ZZ[x])`)
  - Fixed `Poly` initialized with `FracElement` raising `SympifyError`.
  (e.g. `dom = ZZ.frac_field(x); Poly(dom(x+2), y, domain=dom)`)
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[codecov]

Codecov Report

Merging #19659 into master will increase coverage by 0.007%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master    #19659       +/-   ##
=============================================
+ Coverage   75.660%   75.667%   +0.007%     
=============================================
  Files          658       658               
  Lines       171211    171259       +48     
  Branches     40412     40423       +11     
=============================================
+ Hits        129539    129588       +49     
+ Misses       35999     35997        -2     
- Partials      5673      5674        +1     

[smichr]

OK, this appears to be a step in the right direction.