Multi root support for extensions management #29242
Description
Workspace recommendations
Today we scan for a extensions.json inside the workspace .vscode folder: https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/parts/extensions/browser/extensionsActions.ts#L1227 and also here https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/parts/extensions/electron-browser/extensionTipsService.ts#L71
This does not work in a multi root environment. I think we should instead go over all root folders and collect all extensions that are recommended.