Add support for $$ in CREATE FUNCTION for generic dialect

[milenkovicm]

At the moment generic dialect does not support $$ in CREATE FUNCTION .. AS, would it make sense supporting it?

It should be straight forward adding support for it

diff --git a/src/parser/mod.rs b/src/parser/mod.rs
index a719056..5bdaf5c 100644
--- a/src/parser/mod.rs
+++ b/src/parser/mod.rs
@@ -5954,7 +5954,7 @@ impl<'a> Parser<'a> {
     pub fn parse_function_definition(&mut self) -> Result<FunctionDefinition, ParserError> {
         let peek_token = self.peek_token();
         match peek_token.token {
-            Token::DollarQuotedString(value) if dialect_of!(self is PostgreSqlDialect) => {
+            Token::DollarQuotedString(value) if dialect_of!(self is PostgreSqlDialect | GenericDialect) => {
                 self.next_token();
                 Ok(FunctionDefinition::DoubleDollarDef(value.value))
             }
diff --git a/tests/sqlparser_postgres.rs b/tests/sqlparser_postgres.rs
index 9de4b98..033ae6f 100644
--- a/tests/sqlparser_postgres.rs
+++ b/tests/sqlparser_postgres.rs
@@ -3335,7 +3335,7 @@ fn parse_create_function() {
 
     let sql = r#"CREATE OR REPLACE FUNCTION increment(i INTEGER) RETURNS INTEGER LANGUAGE plpgsql AS $$ BEGIN RETURN i + 1; END; $$"#;
     assert_eq!(
-        pg().verified_stmt(sql),
+        pg_and_generic().verified_stmt(sql),
         Statement::CreateFunction {
             or_replace: true,
             temporary: false,