Remove js.ExecutionWorld

The ExecutionWorld doesn't do anything meaningful. It doesn't map to, or
abstract any, v8 concepts. It creates a js.Context, destroys the context and
points to the context. Those all all things the Env can do (and it isn't like
the Env is over-burdened as-is).

Plus the benefit of going through the Env is that we can track/collect all
known Contexts for an isolate in 1 place (the Env), which can facilitate things
like context creation/deletion notifications.

src/cdp/domains/dom.zig

@@ -288,7 +288,7 @@ fn resolveNode(cmd: anytype) !void {
             ls.?.deinit();
             ls = null;
 
-            const ctx = &(isolated_world.executor.context orelse return error.ContextNotFound);
+            const ctx = (isolated_world.context orelse return error.ContextNotFound);
             ls = undefined;
             ctx.localScope(&ls.?);
             if (ls.?.local.debugContextId() == context_id) {