Translations:Extension:Graph/Plans/41/en

Create a converter that would migrate Vega 2-based graphs to be compatible with Vega 5. @Jdlrobson started work on an initial approach in T335048#8794138. The initial work needs to be restructured slightly to refocus it on being an aid to manual porting, instead of the automatic translator which was its original goal. ''Note: We estimate this converter currently works for ~80% of graphs, with diminishing returns on additional engineering effort to cover more. We do not plan on continuing to invest significant additional engineering resources here, but instead to simply repurpose the existing codebase as an aid to manual porting.''