Given the name (a term label) of a term in a model, identify if the term is a
factor term or numeric. This is useful when considering interactions, where
terms like `fac1:fac2`

or `num1:fac1`

may be requested by the user. Only for
terms of the type `fac1:fac2`

will this function return `TRUE`

.

## Usage

```
is_factor_term(object, term, ...)
# S3 method for class 'terms'
is_factor_term(object, term, ...)
# S3 method for class 'gam'
is_factor_term(object, term, ...)
# S3 method for class 'bam'
is_factor_term(object, term, ...)
# S3 method for class 'gamm'
is_factor_term(object, term, ...)
# S3 method for class 'list'
is_factor_term(object, term, ...)
```