Support multiple column names in a field expression

Dare is unable to support multiple column names within the same Field Expression.

i.e.

[{
	// Can't have both fist_name and last_name in the same field expression string
	`displayName`: 'CONCAT(first_name, last_name)`
}]

• Field expressions at the same model level should be straight forward to implement.
• Cross models field expressions would be much harder to implement given how Dare constructs a tree representation where each node on the tree has the field expressions and the table definition which is required.