LibJS: Introduce "dictionary" mode for object shapes

This is similar to "unique" shapes, which were removed in commit
3d92c26445.

The key difference is that dictionary shapes don't have a serial number,
but instead have a "cacheable" flag.

Shapes become dictionaries after 64 transitions have occurred, at which
point no further transitions occur.

As long as properties are only added to a dictionary shape, it remains
cacheable. (Since if we've cached the shape pointer in an IC somewhere,
we know the IC is still valid.)

Deleting a property from a dictionary shape causes it to become an
uncacheable dictionary.

Note that deleting a property from a non-dictionary shape still performs
a delete transition.

This fixes an issue on Discord where Object.freeze() would eventually
OOM us, since they add more than 16000 properties to a single object
before freezing it.

It also yields a 15% speedup on Octane/pdfjs.js :^)

Userland/Libraries/LibJS/Tests/builtins/Object/Object.freeze.js

@@ -75,3 +75,11 @@ test("does not override frozen function name", () => {
     const obj = Object.freeze({ name: func });
     expect(obj.name()).toBe(12);
 });
+
+test("freeze with huge number of properties doesn't crash", () => {
+    const o = {};
+    for (let i = 0; i < 50_000; ++i) {
+        o["prop" + i] = 1;
+    }
+    Object.freeze(o);
+});