CrashReporter: Move progressbar into main window

Previously we would create a temporary progress window to show a
progressbar while the coredump is processed. Since we're only waiting
on backtraces and CPU register states, we can move the progressbar
into the main window and show everything else immediately while the
slow parts are generated in a BackgroundAction.

Userland/Applications/CrashReporter/CrashReporterWindow.gml

@@ -73,8 +73,14 @@
         }
     }
 
+    @GUI::Progressbar {
+        name: "progressbar"
+        text: "Generating crash report: "
+    }
+
     @GUI::TabWidget {
         name: "tab_widget"
+        visible: false
     }
 
     @GUI::Widget {