gh-35043: fix the method monomials_of_degree
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Fixes #35042.
The goal of this PR is to fix two bugs of the method
`monomials_of_degree`. First, the code does not take into account the
case of weighted polynomial ring:
```
sage: P = PolynomialRing(QQ, 3, 'x,y,z', order=TermOrder('wdeglex',
[4,5,6]))
sage: P.inject_variables()
Defining x, y, z
sage: x.degree()
4
sage: P.monomials_of_degree(1)
[x, y, z]
```
Next, as pointed out by @videlec, the current list of monomial that is
returned is not sorted:
```
sage: R.<x,y,z> = ZZ[]
sage: mons = R.monomials_of_degree(2)
sage: mons
[x^2, x*y, x*z, y^2, y*z, z^2]
sage: sorted(mons)
[z^2, y*z, x*z, y^2, x*y, x^2]
sage:
```
CC: @videlec, @yyyyx4
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URL: https://github.com/sagemath/sage/pull/35043
Reported by: David Ayotte
Reviewer(s):
