webpack: make lavamoat work so we can build --env=production builds

[davidmurdoch]

This is already a work in progress.

Related: #26254

[davidmurdoch]

The lavamoat plugin will be responsible for injecting ses and calling lockdown. We need to figure out if we want to remove the --lockdown option from webpack. I vote for complete removal of the option (effectively making --lavamoat the same as doing --lavamoat --lockdown).

We might need to tweak how lockdown-more.js is injected into the bundle, as well as how snow and use-snow are bundled. Wrapping these in lavamoat runtime would cause problems.