tests, expression: move integration test in expression pkg to tests/integrationtest (pingcap#47059)

close pingcap#46679

Author: Defined2014

.gitattributes

@@ -4,5 +4,7 @@
 # Declare files that will always have LF line endings on checkout.
 *.y text eol=lf
 
+*.result diff
+
 util/collate/unicode_0*_ci.go linguist-generated=true
 util/collate/ucadata/unicode_*_data.go linguist-generated=true

expression/BUILD.bazel

@@ -171,7 +171,6 @@ go_test(
         "builtin_vectorized_test.go",
         "collation_test.go",
         "column_test.go",
-        "constant_fold_test.go",
         "constant_test.go",
         "distsql_builtin_test.go",
         "evaluator_test.go",