fix: Handle double quotes inside quoted identifiers correctly (#411)

* fix: Handle double quotes inside quoted identifiers correctly

This fixes #410 for standard SQL, however I don't know enough about other dialects to know if they
handle this differently. May need more extensive testing as well.

* refactor: Make quoted identifier parsing a seperate function

* test: Check that quoted identifier tokenization works

Added `pretty_assertions` so that the `assert_eq!` in the tokenization is readable

* test: Check that quoted identifiers work in mysql

* chore: cargo clippy

tests/sqlparser_mysql.rs

@@ -178,6 +178,37 @@ fn parse_quote_identifiers() {
     }
 }
 
+#[test]
+fn parse_quote_identifiers_2() {
+    let sql = "SELECT `quoted `` identifier`";
+    assert_eq!(
+        mysql().verified_stmt(sql),
+        Statement::Query(Box::new(Query {
+            with: None,
+            body: SetExpr::Select(Box::new(Select {
+                distinct: false,
+                top: None,
+                projection: vec![SelectItem::UnnamedExpr(Expr::Identifier(Ident {
+                    value: "quoted ` identifier".into(),
+                    quote_style: Some('`'),
+                }))],
+                from: vec![],
+                lateral_views: vec![],
+                selection: None,
+                group_by: vec![],
+                cluster_by: vec![],
+                distribute_by: vec![],
+                sort_by: vec![],
+                having: None,
+            })),
+            order_by: vec![],
+            limit: None,
+            offset: None,
+            fetch: None,
+        }))
+    );
+}
+
 #[test]
 fn parse_unterminated_escape() {
     let sql = r#"SELECT 'I\'m not fine\'"#;