Utils: Use numberedKey(Key, int) more wildly

Will ease transition to a key class that doen's have ::number()

Change-Id: Ib2f2957c916f41b0731a2033422bfbf7e429bcc8
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/mesonprojectmanager/toolssettingsaccessor.cpp

@@ -23,7 +23,7 @@ namespace Internal {
 
 static Key entryName(int index)
 {
-    return Constants::ToolsSettings::ENTRY_KEY + Key::number(index);
+    return numberedKey(Constants::ToolsSettings::ENTRY_KEY, index);
 }
 
 ToolsSettingsAccessor::ToolsSettingsAccessor()