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/Libraries/LibGfx/Painter.cpp

@@ -1476,7 +1476,7 @@ void do_draw_text(const IntRect& rect, const TextType& text, const Font& font, T
         lines.append(line);
     }
 
-    static const int line_spacing = 4;
+    constexpr int line_spacing = 4;
     int line_height = font.glyph_height() + line_spacing;
     IntRect bounding_rect { 0, 0, 0, (static_cast<int>(lines.size()) * line_height) - line_spacing };