Make saner the tab completion of INSERT and DELETE in psql

When specified directly as DML queries, INSERT was not getting always
completed to "INSERT INTO", same for DELETE with "DELETE FROM".  This
makes the completion behavior more consistent for both commands, saving
a few keystrokes.

Commands on policies, triggers, grant/revoke, etc. require only DELETE
as completion keyword.

Author: Haiying Tang
Reviewed-by: Dilip Kumar, Julien Rouhaud
Discussion: https://postgr.es/m/OS0PR01MB61135AE2B07CCD1AB8C6A0F6FB549@OS0PR01MB6113.jpnprd01.prod.outlook.com

src/bin/psql/tab-complete.c

@@ -1491,7 +1491,7 @@ psql_completion(const char *text, int start, int end)
 		"ABORT", "ALTER", "ANALYZE", "BEGIN", "CALL", "CHECKPOINT", "CLOSE", "CLUSTER",
 		"COMMENT", "COMMIT", "COPY", "CREATE", "DEALLOCATE", "DECLARE",
 		"DELETE FROM", "DISCARD", "DO", "DROP", "END", "EXECUTE", "EXPLAIN",
-		"FETCH", "GRANT", "IMPORT FOREIGN SCHEMA", "INSERT", "LISTEN", "LOAD", "LOCK",
+		"FETCH", "GRANT", "IMPORT FOREIGN SCHEMA", "INSERT INTO", "LISTEN", "LOAD", "LOCK",
 		"MOVE", "NOTIFY", "PREPARE",
 		"REASSIGN", "REFRESH MATERIALIZED VIEW", "REINDEX", "RELEASE",
 		"RESET", "REVOKE", "ROLLBACK",
@@ -2386,7 +2386,7 @@ psql_completion(const char *text, int start, int end)
 								   " UNION ALL SELECT '('");
 	/* Complete COPY ( with legal query commands */
 	else if (Matches("COPY|\\copy", "("))
-		COMPLETE_WITH("SELECT", "TABLE", "VALUES", "INSERT", "UPDATE", "DELETE", "WITH");
+		COMPLETE_WITH("SELECT", "TABLE", "VALUES", "INSERT INTO", "UPDATE", "DELETE FROM", "WITH");
 	/* Complete COPY <sth> */
 	else if (Matches("COPY|\\copy", MatchAny))
 		COMPLETE_WITH("FROM", "TO");
@@ -3080,7 +3080,7 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("FOR");
 
 /* DELETE --- can be inside EXPLAIN, RULE, etc */
-	/* ... despite which, only complete DELETE with FROM at start of line */
+	/* Complete DELETE with "FROM" */
 	else if (Matches("DELETE"))
 		COMPLETE_WITH("FROM");
 	/* Complete DELETE FROM with a list of tables */
@@ -3208,7 +3208,7 @@ psql_completion(const char *text, int start, int end)
  * EXPLAIN [ ANALYZE ] [ VERBOSE ] statement
  */
 	else if (Matches("EXPLAIN"))
-		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "DECLARE",
+		COMPLETE_WITH("SELECT", "INSERT INTO", "DELETE FROM", "UPDATE", "DECLARE",
 					  "ANALYZE", "VERBOSE");
 	else if (HeadMatches("EXPLAIN", "(*") &&
 			 !HeadMatches("EXPLAIN", "(*)"))
@@ -3227,12 +3227,12 @@ psql_completion(const char *text, int start, int end)
 			COMPLETE_WITH("TEXT", "XML", "JSON", "YAML");
 	}
 	else if (Matches("EXPLAIN", "ANALYZE"))
-		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "DECLARE",
+		COMPLETE_WITH("SELECT", "INSERT INTO", "DELETE FROM", "UPDATE", "DECLARE",
 					  "VERBOSE");
 	else if (Matches("EXPLAIN", "(*)") ||
 			 Matches("EXPLAIN", "VERBOSE") ||
 			 Matches("EXPLAIN", "ANALYZE", "VERBOSE"))
-		COMPLETE_WITH("SELECT", "INSERT", "DELETE", "UPDATE", "DECLARE");
+		COMPLETE_WITH("SELECT", "INSERT INTO", "DELETE FROM", "UPDATE", "DECLARE");
 
 /* FETCH && MOVE */
 
@@ -3587,7 +3587,7 @@ psql_completion(const char *text, int start, int end)
 
 /* PREPARE xx AS */
 	else if (Matches("PREPARE", MatchAny, "AS"))
-		COMPLETE_WITH("SELECT", "UPDATE", "INSERT", "DELETE FROM");
+		COMPLETE_WITH("SELECT", "UPDATE", "INSERT INTO", "DELETE FROM");
 
 /*
  * PREPARE TRANSACTION is missing on purpose. It's intended for transaction