refactor: move toolchain registration call to new rules_js_register_toolchains WORKSPACE function

[gregmagolan]

Long term this will all go away once we drop WORKSPACE support in our rule sets.

[jbedard]

What was the major reason for this? I don't recall if we've discussed it before?

[gregmagolan]

What was the major reason for this? I don't recall if we've discussed it before?

Primarily because we're sneaking in toolchain registrations in WORKSPACE in npm_translate_lock and npm_import which is not a great convention and bad layering. In theory a user could use rules_js without npm_translate_lock and npm_import and they would have to look into the implementation of npm_translate_lock to see what toolchains are needed. Adding an explicity rules_js_configure makes rules_js more like other rule sets where toolchains are registered explicitly in WORKSPACE and not implicitly in an unrelated repository rule.