Expand Expr to support RowExpression type functions (Rex)

[jdye64]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Expr instances are currently missing and reference to RowExpression categorization or extraction. Functions should be added to categorize Expr instances and support functionality around them.

Describe the solution you'd like
Update expr.rs to include functions for RowExpression type operations

Describe alternatives you've considered
None

Additional context
None