Frames on the same origin share v8 data

Depends on: https://github.com/lightpanda-io/zig-v8-fork/pull/153

In some ways this is an extension of
https://github.com/lightpanda-io/browser/pull/1635 but it has more implications
with respect to correctness.

A js.Context wraps a v8::Context. One of the important thing it adds is the
identity_map so that, given a Zig instance we always return the same v8::Object.

But imagine code running in a frame. This frame has its own Context, and thus
its own identity_map. What happens when that frame does:

```js
window.top.frame_loaded = true;
```

From Zig's point of view, `Window.getTop` will return the correct Zig instance.
It will return the *Window references by the "root" page. When that instance is
passed to the bridge, we'll look for the v8::Object in the Context's
`identity_map` but wont' find it. The mapping exists in the root context
`identity_map`, but not within this frame. So we create a new v8::Object and now
our 1 zig instance has N v8::Objects for every page/frame that tries to access
it.

This breaks cross-frame scripting which should work, at least to some degree,
even when frames are on the same origin.

This commit adds a `js.Origin` which contains the `identity_map`, along with our
other `v8::Global` storage. The `Env` now contains a `*js.Origin` lookup,
mapping an origin string (e.g. lightpanda.io:443) to an *Origin. When a Page's
URL is changed, we call `self.js.setOrigin(new_url)` which will then either get
or create an origin from the Env's origin lookup map.

js.Origin is reference counted so that it remains valid so long as at least 1
frame references them.

There's some special handling for null-origins (i.e. about:blank). At the root,
null origins get a distinct/isolated Origin. For a frame, the parent's origin
is used.

Above, we talked about `identity_map`, but a `js.Context` has 8 other fields
to track v8 values, e.g. `global_objects`, `global_functions`,
`global_values_temp`, etc. These all must be shared by frames on the same
origin. So all of these have also been moved to js.Origin. They've also been
merged so that we now have 3 fields: `identity_map`, `globals` and `temps`.

Finally, when the origin of a context is changed, we set the v8::Context's
SecurityToken (to that origin). This is a key part of how v8 allows cross-
context access.

build.zig.zon

@@ -5,10 +5,10 @@
     .minimum_zig_version = "0.15.2",
     .dependencies = .{
         .v8 = .{
-            .url = "https://github.com/lightpanda-io/zig-v8-fork/archive/refs/tags/v0.3.1.tar.gz",
-            .hash = "v8-0.0.0-xddH64J7BAC81mkf6G9RbEJxS-W3TIRl5iFnShwbqCqy",
+            .url = "https://github.com/lightpanda-io/zig-v8-fork/archive/refs/tags/v0.3.2.tar.gz",
+            .hash = "v8-0.0.0-xddH6wx-BABNgL7YIDgbnFgKZuXZ68yZNngNSrV6OjrY",
         },
-        //.v8 = .{ .path = "../zig-v8-fork" },
+        // .v8 = .{ .path = "../zig-v8-fork" },
         .brotli = .{
             // v1.2.0
             .url = "https://github.com/google/brotli/archive/028fb5a23661f123017c060daa546b55cf4bde29.tar.gz",