Implement DOMPoint and DOMPointReadOnly

Passes some but not all WPT tests. One failure is caused by an issue in codegen for the `DOMPointInit` dictionary, the others by outdated tests: Gecko implements an old version of the spec that overloaded the `DOMPoint` constructor to optionally take an object as the first argument, and made `DOMPointReadOnly` non-constructible.

tests/wpt/metadata-css/geometry-1_dev/html/DOMMatrix-001.htm.ini

@@ -0,0 +1,53 @@
+[DOMMatrix-001.htm]
+  type: testharness
+  [testConstructor0]
+    expected: FAIL
+
+  [testConstructor1]
+    expected: FAIL
+
+  [testConstructor2]
+    expected: FAIL
+
+  [testConstructor3]
+    expected: FAIL
+
+  [testConstructor4]
+    expected: FAIL
+
+  [testConstructor5]
+    expected: FAIL
+
+  [testConstructor6]
+    expected: FAIL
+
+  [testConstructor7]
+    expected: FAIL
+
+  [testConstructor8]
+    expected: FAIL
+
+  [testConstructor9]
+    expected: FAIL
+
+  [testConstructor10]
+    expected: FAIL
+
+  [testConstructor11]
+    expected: FAIL
+
+  [testConstructor12]
+    expected: FAIL
+
+  [testConstructor13]
+    expected: FAIL
+
+  [testConstructorIllegal0]
+    expected: FAIL
+
+  [testConstructorIllegal1]
+    expected: FAIL
+
+  [testConstructorIllegal2]
+    expected: FAIL
+