WindowServer: In HighDPI mode, load high-res window buttons and high-res cursors

Bitmap::load_from_file("foo.png", 2) will now look for "foo-2x.png" and
try load that as a bitmap with scale factor 2 if it exists. If it
doesn't, it falls back to the 1x bitmap as normal.
Only places that know that they'll draw the bitmap to a 2x painter
should pass "2" for the second argument.

Use this new API in WindowServer for loading window buttons and
cursors.

As a testing aid, ctrl-shift-super-i can force HighDPI icons off in
HighDPI mode. Toggling between low-res and high-res icons makes it easy
to see if the high-res version of an icon looks right: It should look
like the low-res version, just less jaggy.

We'll likely have to grow a better API for loading scaled resources, but
for now this suffices.

Things to check:
- `chres 640 480` followed by `chres 640 480 2` followed by
  `chres 640 480`
- window buttons in window context menu (in task bar and on title bar)
  still have low-res icons
- ctrl-shift-super-i in high-res mode toggles sharpness of window
  buttons and of arrow cursorf
- arrow cursor hotspot is still where you'd expect

Userland/Services/WindowServer/Cursor.cpp

@@ -46,7 +46,8 @@ CursorParams CursorParams::parse_from_file_name(const StringView& cursor_path, c
     auto params_str = file_title.substring_view(last_dot_in_title.value() + 1);
 
     CursorParams params(default_hotspot);
-    for (size_t i = 0; i + 1 < params_str.length();) {
+    bool in_display_scale_part = false;
+    for (size_t i = 0; i + 1 < params_str.length() && !in_display_scale_part;) {
         auto property = params_str[i++];
 
         auto value = [&]() -> Optional<size_t> {
@@ -88,6 +89,9 @@ CursorParams CursorParams::parse_from_file_name(const StringView& cursor_path, c
             else
                 dbgln("Cursor frame rate outside of valid range (100-1000ms)");
             break;
+        case '-':
+            in_display_scale_part = true;
+            break;
         default:
             dbg() << "Ignore unknown property '" << property << "' with value " << value.value() << " parsed from cursor path: " << cursor_path;
             return { default_hotspot };