CASE THEN/ELSE {value expression} (#7810)

## Rationale
There has been a long running issue where some operators in THEN/ELSE
expressions have unexpectedly required parentheses.

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## Changes
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## Tasks 📍
- [ ] Claude Code Review
- [ ] Manual Testing
- [ ] Test Automation
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Author: labkey-matthewb

query/src/org/labkey/query/QueryTestCase.jsp

@@ -911,8 +911,10 @@ d,seven,twelve,day,month,date,duration,guid
                 assertFalse(rs.getColumn(1).isHidden());
                 assertEquals("0.00", rs.getColumn(1).getFormat());
             }
-        }
+        },
 
+        // test operators in THEN expression
+        new SqlTest("SELECT CASE WHEN 1=1 THEN 'a' || 'b' ELSE 'x' || 'y' END")
     );
 
     List<SqlTest> postgres = List.of(

query/src/org/labkey/query/sql/SqlBase.g

@@ -729,15 +729,15 @@ caseExpression
 	;
 
 whenClause
-	: (WHEN^ logicalExpression THEN! unaryExpression)
+	: (WHEN^ logicalExpression THEN! valueExpression)
 	;
 
 altWhenClause
-	: (WHEN^ unaryExpression THEN! unaryExpression)
+	: (WHEN^ unaryExpression THEN! valueExpression)
 	;
 
 elseClause
-	: (ELSE^ unaryExpression)
+	: (ELSE^ valueExpression)
 	;