YUL tree visitor interface (#369)

- Implement the visitor interface. This simplifies working with the AST,
for example transformations into other IRs or collecting and analyzing
various statistics.
- Switch the explorer to use the visitor interface.
- Add the reciprocal function name conversion for function names.
- Some drive-by cosmetic fixes.

---------

Signed-off-by: xermicus <bigcyrill@hotmail.com>

crates/yul/src/parser/statement/function_definition.rs

@@ -18,6 +18,8 @@ use crate::parser::error::Error as ParserError;
 use crate::parser::identifier::Identifier;
 use crate::parser::statement::block::Block;
 use crate::parser::statement::expression::function_call::name::Name as FunctionName;
+use crate::visitor::AstNode;
+use crate::visitor::AstVisitor;
 
 /// The function definition statement.
 /// All functions are translated in two steps:
@@ -329,6 +331,28 @@ where
     }
 }
 
+impl AstNode for FunctionDefinition {
+    fn accept(&self, ast_visitor: &mut impl AstVisitor) {
+        ast_visitor.visit_function_definition(self);
+    }
+
+    fn visit_children(&self, ast_visitor: &mut impl AstVisitor) {
+        for argument in &self.arguments {
+            argument.accept(ast_visitor);
+        }
+
+        self.body.accept(ast_visitor);
+
+        for result in &self.result {
+            result.accept(ast_visitor);
+        }
+    }
+
+    fn location(&self) -> Location {
+        self.location
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use std::collections::BTreeSet;