Add localization for loader and startup via core/__locales__

[dpvc]

this PR adds localization to the loader and startup modules. It does so by adding a core/__locales__ directory for the core component, and using that for their messages, since the loader and startup components include the core component. These components now load core/locale.js before lib/loader.js or lib/startup.js so that the Locale.isComponent value is set before the files imported by the lib code (in particular, their Component.js files) are loaded. Otherwise Locale might use the wrong directory when trying to find the localization files.

Copying the core localization has been added to the package scripts, and I've also taken this opportunity to adjust the copy:assets and copy:locales scripts to use a list of sub-scripts to run rather than having them explicitly called. This allows new ones to be added easier, and also to make mjs the default for $1 so you can just use pnpm -s copy:assets without needing to specify mjs directly.

The rest is just the changes to localize the messages in loader.ts and startup.ts.