@openctx/vscode-lib controller doesn't work in web worker context

[vovakulikov]

In some consumers (like Cody Web) it should be possible to run/create openctx controller within
web worker, at the moment since init logic here https://github.com/sourcegraph/openctx/blob/main/client/vscode-lib/src/global.ts uses global. statement it breaks initialisation for Cody Web.

As a temporal workaround, I added self.global = {} to avoid this problem in Cody Web, but eventually, I think a fix should be done here, maybe instead of global.openctx we could share vscode API through singleton