Merged PR 795016: Enable QTest in light UTs

Due to bug #2195273 , QTest has been disabled in our selfhost builds. The problem is that we no longer exercise QTest framework in our selfhost, while at the same time we're deploying QTest to customers. Also, because there's no QTest UTs, the (optional) QTest validation stage in our release pipeline failed.

To address the above problem, this PR enables some of light UTs, e.g., UTs that don't have many `[InlineData]` attributes and that don't take a long time to run.

Related work items: #2195273

Public/Src/Utilities/UnitTests/Collections/Test.BuildXL.Utilities.Collections.dsc

@@ -1,5 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
+import * as QTest from "Sdk.Managed.Testing.QTest";
+import * as XUnit from "Sdk.Managed.Testing.XUnit";
 
 namespace Collections {
     @@public
@@ -11,5 +13,8 @@ namespace Collections {
             importFrom("BuildXL.Utilities").Native.dll,
             importFrom("BuildXL.Utilities").Utilities.Core.dll,
         ],
+        testFramework: BuildXLSdk.Flags.isMicrosoftInternal
+            ? QTest.getFramework(XUnit.framework)
+            : undefined
     });
 }

Public/Src/Utilities/UnitTests/Configuration/Test.BuildXL.Utilities.Configuration.dsc

@@ -1,5 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
+import * as QTest from "Sdk.Managed.Testing.QTest";
+import * as XUnit from "Sdk.Managed.Testing.XUnit";
 
 namespace Configuration {
     @@public
@@ -12,6 +14,9 @@ namespace Configuration {
             importFrom("BuildXL.Utilities").dll,
             importFrom("BuildXL.Utilities").Configuration.dll,
             importFrom("BuildXL.Utilities").Utilities.Core.dll,
-        ]
+        ],
+        testFramework: BuildXLSdk.Flags.isMicrosoftInternal
+            ? QTest.getFramework(XUnit.framework)
+            : undefined
     });
 }