feat: add main.crdt

[cazala]

Let the Editor create an empty main.crdt file when it's being activated if the project doesn't have one. This is so the subsequent sdk commands, like the dev server, work properly (the have special logic for Editor projects based on this file bieng present). This fixes the issue where Smart Items were not visible on the Visual Editor on projects that were created without using the Editor.

[github-actions[bot]]

Test this pull request

• The editor-sdk7 extension can be tested in VSCode by downloading this package and running:

  code --force --install-extension editor-sdk7.vsix