Add transform functionality for AST manipulation

[rantibi]

I would like to propose adding a transform functionality to enable easier manipulation of the Abstract Syntax Tree (AST).
This feature would allow users to traverse and modify the AST without having to implement complex tree traversal logic themselves.

The proposed functionality would be similar to the transform method available in sqlglot, a Python SQL parser and transpiler. In sqlglot, users can apply a transformation function to each node in the parsed expression tree.

Example of how it could work in node-sql-parser:

const ast = parser.astify('SELECT * FROM users');
const transformedAst = parser.transform(ast, (expr) => {
  if (expr.type === 'column_ref') {
    return {
      type: "column_ref",
      table: "new_table",
      column: "new_column",
    };
  }
  return expr;
});

const transformedSql = parser.sqlify(transformedAst);

This would allow users to easily modify the AST for various purposes, such as:

• Renaming tables or columns
• Adding or removing clauses
• Modifying expressions
• Implementing custom SQL transformations

Reference:
sqlglot's transform functionality