feat(regular_expression): implement visitor pattern trait for regex A…

…ST (#6055)

- resolves #5977
- supersedes #5951

To facilitate easier traversal of the Regex AST, this PR defines a `Visit` trait with default implementations that will walk the entirety of the Regex AST. Methods in the `Visit` trait can be overridden with custom implementations to do things like analyzing only certain nodes in a regular expression, which will be useful for regex-related `oxc_linter` rules.

In the future, we should consider automatically generating this code as it is very repetitive, but for now a handwritten visitor is sufficient.

crates/oxc_regular_expression/examples/visitor.rs

@@ -0,0 +1,28 @@
+#![allow(clippy::print_stdout)]
+
+use oxc_allocator::Allocator;
+use oxc_regular_expression::{
+    visit::{RegExpAstKind, Visit},
+    Parser, ParserOptions,
+};
+
+struct TestVisitor;
+
+impl Visit<'_> for TestVisitor {
+    fn enter_node(&mut self, kind: RegExpAstKind) {
+        println!("enter_node: {kind:?}");
+    }
+
+    fn leave_node(&mut self, kind: RegExpAstKind) {
+        println!("leave_node: {kind:?}");
+    }
+}
+
+fn main() {
+    let source_text = r"/(https?:\/\/github\.com\/(([^\s]+)\/([^\s]+))\/([^\s]+\/)?(issues|pull)\/([0-9]+))|(([^\s]+)\/([^\s]+))?#([1-9][0-9]*)($|[\s\:\;\-\(\=])/";
+    let allocator = Allocator::default();
+    let parser = Parser::new(&allocator, source_text, ParserOptions::default());
+    let pattern = parser.parse().unwrap().pattern;
+    let mut visitor = TestVisitor;
+    visitor.visit_pattern(&pattern);
+}

crates/oxc_regular_expression/src/lib.rs

@@ -9,6 +9,7 @@ mod literal_parser;
 mod options;
 mod span;
 mod surrogate_pair;
+pub mod visit;
 
 mod generated {
     mod derive_clone_in;