LibWeb: Annotate which CSS properties may affect layout

This patch adds CSS::property_affects_layout(PropertyID) which tells us
whether a CSS property would affect layout if it were changed.

This will be used to avoid unnecessary relayout work when something
changes that really only requires us to repaint the page.

To mark a property as not affecting layout, set "affects-layout" to
false in the corresponding Properties.json entry. Note that all
properties affect layout by default.

Userland/Libraries/LibWeb/CSS/Properties.json

@@ -43,6 +43,7 @@
     ]
   },
   "background-color": {
+    "affects-layout": false,
     "inherited": false,
     "initial": "transparent",
     "valid-types": [
@@ -501,6 +502,7 @@
     ]
   },
   "color": {
+    "affects-layout": false,
     "inherited": true,
     "initial": "-libweb-palette-base-text",
     "valid-types": [
@@ -1049,6 +1051,7 @@
     ]
   },
   "outline-width": {
+    "affects-layout": false,
     "inherited": false,
     "initial": "medium",
     "valid-types": [
@@ -1243,6 +1246,7 @@
   },
   "text-decoration-line": {
     "__comment": "FIXME: This property is not supposed to be inherited, but we currently rely on inheritance to propagate decorations into line boxes.",
+    "affects-layout": false,
     "inherited": true,
     "initial": "none",
     "valid-identifiers": [