Bundle https-everywhere in tor-browser instead of tor-browser-build

Followup from #40091 (closed) and tor-browser-build#40073 (closed): we should try to bundle the builtin https-everywhere extension entirely in tor-browser and avoid the parts in tor-browser-build. I tried this with a Makefile.in that unzipped the xpi into dist/fennec/assets/extensions/https-everywhere, but there was some unexpected behaviour, see !42 (comment 2708014). We should investigate and fix this.