Localise media paths in walkthroughs

[PeterWone]

For context see microsoft/vscode-l10n#180

Strings directly defined in walkthroughs can be localised with the usual %walkthroughs.mykey% mechanism.

However, walkthroughs depend heavily on references to resources like images and Markdown documents.

  "walkthroughs.howToPrint.title": "Premiers pas avec l’impression",
  "walkthroughs.howToPrint.description": "Découvrez l’impression dans l’éditeur pour le code source et la documentation.",
  "walkthroughs.steps.printEditorActive.title": "Imprimer l’intégralité du contenu de l’éditeur actif",
  "walkthroughs.steps.printEditorActive.media": "assets/print-entier-content-editeur-actif.fr.md",

As you can see in the above excerpt from a package.nls.fr.json, the path to walkthroughs.steps.printEditorActive.media was inappropriately localised.

After some discussion on the linked issue, our tentative proposal is

1. Define a token {locale}
2. Path strings requiring this kind of localisation are marked by the presence of {locale}
3. Localise them by replacing the token with the locale code for each generated file

This approach makes no assumptions about the structure of the resource path; the locale might name a directory, or it might be part of the filename. It does require that resource filenames for the default language have literal {locale} in the name or path. The below examples are in the context of contributed settings in package.json

  "walkthroughs.steps.printEditorActive.media": "assets/print-entire-content-active-editor.{locale}.md",

or

  "walkthroughs.steps.printEditorActive.media": "assets/{locale}/print-entire-content-active-editor.md",

This should extend to the properties of object values.

"media": {
	"image": "media/image.{locale}.png",
	"altText": "%walkthroughs.foo.media.altText%"
},