Support `${outDir}` macro from imports coming from Fable.Compiler plugins

[MangelMaxime]

Description

Fable imports allows to use ${outDir} macro, in order to make the import path be adapted to reference independently from where we consume the imported code.

However, it seems that import coming from Plugin doesn't support that ${outDir} maccro.

More context there https://github.com/Zaid-Ajaj/Feliz/issues/624