Support for projection item prefix operator (CONNECT_BY_ROOT)

[tomershaniii]

Support for the snowflake CONNECT_BY_ROOT operator
https://docs.snowflake.com/en/sql-reference/constructs/connect-by

[iffyio]

Suggested change

	//Select item operators
	/// Select item operators

for the doc comment can we describe what the function does?

[iffyio]

Thinking introducing the prefix field into the select item is a bit more invasive and would be nice to avoid if it makes sense. I noticed this use case is similar in representation to IntroducedString, maybe we can repurpose that one to be generic.

I'm thinking something like this?

changing that enum variant into

Expr::Prefixed { prefix: Ident, expr: Expr }

Then impl wise here we could wrap the self.parse_wildcard_expr() call with the logic to optionally parse the prefix

fn parse_select_item_expr() {
  let prefix = self.parse_one_of_keywords(self.dialect.get_reserved_keywords_for_select_item());

  let expr = self.parse_wildcard_expr()?

  if let Some(prefix) = prefix {
    Expr::Prefixed {
      prefix: Ident::new(prefix),
      expr,
    }
  } else {
    expr
  }
}

[iffyio]

could we move this to the top of the file maybe? thinking it would be more visible there and if the list happens to get long it doesnt add to the function's length