LibWeb: Resolve calc() values in CSS transform

There are two parts to this fix:

- First, StyleProperties::transformations() would previously omit calc()
  values entirely when returning the list of transformations. This was
  very confusing to StackingContext which then tried to index into the
  list based on faulty assumptions. Fix this by emitting calc values.

- Second, StackingContext::get_transformation_matrix() now always calls
  resolve() on length-percentages. This takes care of actually resolving
  calc() values. If no reference value for percentages is provided, we
  default to 0px.

This stops LibWeb from asserting on websites with calc() in transform
values, such as https://qt.io/ :^)

Tests/LibWeb/Layout/input/transform-calc-length-values.html

@@ -0,0 +1,8 @@
+<style>
+body {
+    transform: translate3d(calc(50px), calc(100px), calc(0px));
+    border: 1px solid black;
+    width: 100px;
+    height: 100px;
+}
+</style>