Series: Possible improvements for Order of expressions involving factorials

[anutosh491]

Being a contributor to the series module I have my fair share of idea of what sympy can achieve currently and what are it's limitations. Hence I make this issue thinking what a user would expect out of the following expressions shown below

Following basic pattern of growth of functions which is const < log(x) < x**n < 2**x or exp(x) < factorial(x) < x**x we have
On Master

>>> O(2**x + factorial(x), (x, oo))
O(exp(x*log(2)) + factorial(x), (x, oo))

>>> O(2**x + factorial(x) + x**x, (x, oo))
O(exp(x*log(x)) + factorial(x), (x, oo))

>>> O(x + factorial(x), (x, oo))
O(x*(1 + factorial(x)/x), (x, oo))

Expected Results: I also ended up checking the results on other CAS and If i remember the results worked properly on diofant

>>> O(2**x + factorial(x), (x, oo)) 
O(factorial(x), (x, oo))

>>> O(2**x + factorial(x) + x**x, (x, oo))
O((1/x)**(-x), (x, oo))

>>> O(x + factorial(x), (x, oo))
O( factorial(x) , (x, oo))

[anutosh491]

One of my Pr which for order which is under review #22247 (where the original issue has been addressed but we have been trying to extend our thinking to some mutlivariate cases) solves the first 2 of these but the 3rd one still remains the same !