LibWeb: Exclude table-wrapper margins from table available width

Table should not take up more width than is available inside wrapper
after margins are taken in account.

Tests/LibWeb/Layout/input/table/fixed-margins.html

@@ -0,0 +1,22 @@
+<style>
+* {
+    font-family: 'SerenitySans';
+}
+
+.wrapper {
+    background-color: mediumturquoise;
+}
+
+.box {
+    display: table;
+    background-color: orange;
+    margin-left: 100px;
+    margin-right: 100px;
+}
+
+.cell {
+    display: table-cell;
+}
+  </style>
+  <div class="wrapper"><div class="box"><div class="cell">DaTa DisplaYiNg CSS WeBpaGE ScReEn OF aR AddITioN COmmOnLY To AdJuSt PRiCiNG sTYLiNG ceLL oF TAbLeS  
+  </div></div></div>