Unified parallelBabel API

[ef4]

Both broccoli-babel-transpiler and ember-cli-htmlbars-inline-precompile have invented their own mutually-incompatible solutions for plugin serialization.

broccoli-babel-transpiler allows a _parallelBabel key on any value within the plugin config, which will cause that value to get replaced based on its requireFile, buildWith, params, and/or useMethod properties. Everything but requireFile is optional.

ember-cli-htmlbars-inline-precompile allows a parallelBabel key on only the top-level values within the plugin config, which will cause that value to get replaced based on its requireFile, buildWith, and params, properties, which are all mandatory.

We're now stuck with these, but before this situation gets any worse I want to refactor both of them and embroider to share one library.

[NullVoxPopuli]

is this still an issue? we don't use ec-htmlbars-inline-precompile anymore