Get expected service worker version from renderer instead of main.js

Due to caching, it is possible that a webview ends up running an older service worker than the current renderer version. This can be triggered if a user has webview open, updates vs code (to a version that makes service worker related changes), and then has the webview restored. Depending on what was changed in the service worker, this could potentially break the webview

Previously we tried to avoid this by checking a version number stored in `main.js`. However I don't think this is reliable as `main.js` can also be cached.

The fix here to check the sw version against an expected version from the renderer. In code, these two should always be kept in sync