Painless: Fix Semicolon Regression (#33212)

Trailers (statements following something like an if statement) that don't use brackets currently require a semicolon even if they're the last statement. This is a regression caused by (#29566) and noted by (#33193). This change fixes the regression and adds a test for the broken case.

Author: jdconrad

modules/lang-painless/src/main/antlr/PainlessParser.g4

@@ -22,7 +22,7 @@ parser grammar PainlessParser;
 options { tokenVocab=PainlessLexer; }
 
 source
-    : function* statement* dstatement? EOF
+    : function* statement* EOF
     ;
 
 function
@@ -35,7 +35,7 @@ parameters
 
 statement
     : rstatement
-    | dstatement SEMICOLON
+    | dstatement ( SEMICOLON | EOF )
     ;
 
 // Note we use a predicate on the if/else case here to prevent the