Scriptlet injections from the 2 adblock engines are currently concatenated using just a newline separator. They should instead be enclosed in separate `{...}` scopes. Without this change, definitions (e.g. classes, variables) from one engine's injection could potentially conflict with those from the other engine. This wasn't an issue previously due to serverside dependency bundling within scriptlets, at least until the advent of https://github.com/brave/brave-core-crx-packager/pull/1193.