Implement object literal parsing; Instantiate classes from object literals

Essentially, if the contextual type is a class with a constructor that takes zero arguments or doesn't have a constructor at all, an object literal can be used to initialize a new instance of that class with preset values.

tests/compiler/object-literal.ts

@@ -0,0 +1,26 @@
+import "allocator/arena";
+
+class Foo {
+  bar: i32;
+  baz: string;
+}
+
+function bar(foo: Foo): void {
+  assert(foo.bar == 1);
+  assert(foo.baz == "hello world");
+}
+
+bar({ bar: 1, baz: "hello world" });
+
+class Foo2 {
+  bar: i32;
+  constructor() {
+    this.bar = 1;
+  }
+}
+
+function bar2(foo: Foo2): void {
+  assert(foo.bar == 2);
+}
+
+bar2({ bar: 2 });