Qbs build system: Add a component for test files groups

Mainly in order to enforce a unified group name across QtC libraries and
plugins.

Change-Id: I6eafe0f9d227ec73d8c9029675866c67063768fb
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangformat/clangformat.qbs

@@ -54,10 +54,8 @@ QtcPlugin {
         "clangformatutils.cpp",
     ]
 
-    Group {
-        name: "Tests"
+    QtcTestFiles {
         prefix: "tests/"
-        condition: qtc.testsEnabled
         cpp.defines: outer.concat('TESTDATA_DIR="' + sourceDirectory + "/tests/data" + '"')
         files: [
             "clangformat-test.cpp",