Add more Expand/Reduce functions


## Description

The following Built-in functions have yet to be written: 

* `ExpandNumerator`
* `ExpToTrig`
* `FactorSquareFree`
* `FactorTerms`
* `FunctionExpand`
* `PowerExpand`
* `ToRadicals`
* `TrigExpand`
* `TrigReduce`
* `TrigToExp`

## Priority

Low. I don't know of any package requiring these.

## Additional context

This is a follow-up to a list reported in #1390