use leja order for factored polynomial, follow up on #568

[jverzani]

This adds a leja order to the FactoredPolynomial type when using fromroots.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.80%. Comparing base (d5a472a) to head (a699d85).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #587      +/-   ##
==========================================
+ Coverage   75.77%   75.80%   +0.03%     
==========================================
  Files          38       38              
  Lines        4057     4063       +6     
==========================================
+ Hits         3074     3080       +6     
  Misses        983      983              

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[martinholters]

Should be possible to also test FactoredPolynomial now here:

Polynomials.jl/test/StandardBasis.jl

Lines 988 to 990 in d5a472a

	if P !== FactoredPolynomial
	@test fromroots(P, roots(p)) * p[end] ≈ p
	end