Userland: static vs non-static constexpr variables

Problem:
- `static` variables consume memory and sometimes are less
  optimizable.
- `static const` variables can be `constexpr`, usually.
- `static` function-local variables require an initialization check
  every time the function is run.

Solution:
- If a global `static` variable is only used in a single function then
  move it into the function and make it non-`static` and `constexpr`.
- Make all global `static` variables `constexpr` instead of `const`.
- Change function-local `static const[expr]` variables to be just
  `constexpr`.

Userland/Services/Taskbar/ShutdownDialog.cpp

@@ -5,7 +5,7 @@
  */
 
 #include "ShutdownDialog.h"
-#include <AK/String.h>
+#include <AK/StringView.h>
 #include <AK/Vector.h>
 #include <LibGUI/BoxLayout.h>
 #include <LibGUI/Button.h>
@@ -17,7 +17,7 @@
 #include <LibGfx/FontDatabase.h>
 
 struct Option {
-    String title;
+    StringView title;
     Vector<char const*> cmd;
     bool enabled;
     bool default_action;