Fix samples' arguments to SampleApplication

Two new parameters were added in
https://chromium-review.googlesource.com/c/angle/angle/+/3664916 with
default values, but not all samples were updated to accomodate them.  As
a result, many samples passed in the major version for client type and
thus couldn't run.

This change introduces an enum class for the client type + version to
make sure such a mistake is impossible.

Bug: angleproject:7360
Change-Id: I450edee612d08a7b67530b61615f63268fefb200
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3748413
Auto-Submit: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Lingfeng Yang <lfy@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>

samples/multi_window/MultiWindow.cpp

@@ -20,7 +20,7 @@ class MultiWindowSample : public SampleApplication
 {
   public:
     MultiWindowSample(int argc, char **argv)
-        : SampleApplication("MultiWindow", argc, argv, 2, 0, 256, 256)
+        : SampleApplication("MultiWindow", argc, argv, ClientType::ES2, 256, 256)
     {}
 
     bool initialize() override