Partial Fraction Decomposition

[matthew-mccall]

Is your feature request related to a problem? Please describe.
The ability to perform partial fraction decomposition:

$$ \frac{1}{(s+1)(s+2)} = \frac{A}{s+1}+\frac{B}{s+2} $$

Describe the solution you'd like
We can introduce a an API to perform partial fraction decomposition like so:

Oasis::Divide { /* ... */ } fraction;
auto result = Oasis::DecomposePartialFraction(fraction);

Describe alternatives you've considered
None exists in Oasis at the time of writing.

Additional context
Add any other context or screenshots about the feature request here.