psql: Refine lexing of BEGIN...END blocks in CREATE FUNCTION statements

Only track BEGIN...END blocks if they are in a CREATE [OR REPLACE]
{FUNCTION|PROCEDURE} statement.  Ignore if in parentheses.

Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://www.postgresql.org/message-id/cee01d26fe55bc086b3bcf10bfe4e8d450e2f608.camel@cybertec.at

src/include/fe_utils/psqlscan_int.h

@@ -114,8 +114,14 @@ typedef struct PsqlScanStateData
 	int			paren_depth;	/* depth of nesting in parentheses */
 	int			xcdepth;		/* depth of nesting in slash-star comments */
 	char	   *dolqstart;		/* current $foo$ quote start string */
+
+	/*
+	 * State to track boundaries of BEGIN ... END blocks in function
+	 * definitions, so that semicolons do not send query too early.
+	 */
 	int			identifier_count;	/* identifiers since start of statement */
-	int			begin_depth;	/* depth of begin/end routine body blocks */
+	char		identifiers[4]; /* records the first few identifiers */
+	int			begin_depth;	/* depth of begin/end pairs */
 
 	/*
 	 * Callback functions provided by the program making use of the lexer,