test: Move misc sample shaders to test/samples

Change-Id: I72d25393e499f85733232043fd492c2705e35c68
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51223
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Reviewed-by: David Neto <dneto@google.com>

test/samples/function.wgsl

@@ -0,0 +1,22 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+fn main() -> f32 {
+    return ((2. * 3.) - 4.) / 5.;
+}
+
+[[stage(compute)]]
+[[workgroup_size(2)]]
+fn ep() {
+}