Support babel plugin options in experimentalBabelParserPluginsList

[saaryab]

Hi @byara (or whoever is working on this now),

Thanks for making and maintaining this plugin!

experimentalBabelParserPluginsList allows adding custom babel parser plugins, but it does not allow sending plugin options.

For example, @ShigotoMitame was using the decorators plugin with the following options:

plugins: ['typescript', 'jsx', ['decorators', {'decoratorsBeforeExport': true}], 'classProperties'],

It seems like the preprocessor.js code should allow any type of babel plugin, both a string and an array of [PLUGIN_NAME: string, PLUGIN_OPTIONS: object], but when adding a plugin with options I get the following error:

$ /home/.../project/node_modules/.bin/prettier -w .
[error] Invalid experimentalBabelParserPluginsList value. Expected an array of a string, but received [["decorators", { decoratorsBeforeExport: true }]].
error Command failed with exit code 1.

When adding these options directly in preprocessor.js like @ShigotoMitame did everything works as expected so it looks liek this is a validation issue caused by prettier's options which don't seem to support any complex values:

 * @property {'int' | 'boolean' | 'choice' | 'path'} type

https://github.com/prettier/prettier/blob/5909f5b3f191a0a32f759e1f4378477d3b90e28e/src/main/core-options.js#L17

As a work around I was wondering if you would consider supporting taking the plugins directly from a babelrc file, or at least allowing JSON in the experimentalBabelParserPluginsList array to support plugins with options.

Originally posted by @saaryab in #12 (comment)

[saaryab]

I created a PR with a fix to allow passing JSON options in the experimentalBabelParserPluginsList1 array:
#88

[byara]

PR merged.