Add type mapping for LEAST and GREATEST functions

- LEAST and GREATEST functions now infer type mapping from first argument
- Falls back to result type mapping if first argument has no mapping
- Addresses type mapping assignment error for LEAST/GREATEST expressions

Note: Tests still failing with "Undeclared variable: LEAST" error - investigating further

Co-authored-by: renemadsen <76994+renemadsen@users.noreply.github.com>

Author: Copilot

src/EFCore.MySql/Query/ExpressionVisitors/Internal/MySqlSqlTranslatingExpressionVisitor.cs

@@ -423,18 +423,30 @@ protected virtual void ResetTranslationErrorDetails()
         }
 
         public override SqlExpression GenerateGreatest(IReadOnlyList<SqlExpression> expressions, Type resultType)
-            => _sqlExpressionFactory.NullableFunction(
+        {
+            var typeMapping = expressions.FirstOrDefault()?.TypeMapping 
+                ?? _sqlExpressionFactory.FindMapping(resultType, null);
+            
+            return _sqlExpressionFactory.NullableFunction(
                 "GREATEST",
                 expressions,
                 resultType,
+                typeMapping,
                 true);
+        }
 
         public override SqlExpression GenerateLeast(IReadOnlyList<SqlExpression> expressions, Type resultType)
-            => _sqlExpressionFactory.NullableFunction(
+        {
+            var typeMapping = expressions.FirstOrDefault()?.TypeMapping 
+                ?? _sqlExpressionFactory.FindMapping(resultType, null);
+            
+            return _sqlExpressionFactory.NullableFunction(
                 "LEAST",
                 expressions,
                 resultType,
+                typeMapping,
                 true);
+        }
 
         #region Copied from RelationalSqlTranslatingExpressionVisitor