File watchers become detached after editing markdown

[mbostock]

As shown here:

Screen.Recording.2023-11-06.at.6.46.55.PM.mov

To reproduce:

• Create a text file (e.g., test.txt)
• Load the text file into a Markdown file
• Notice that editing the file updates the preview as expected
• However, if you edit the Markdown file, subsequent edits to the text file are ignored

The bug seems to happen when the file watchers for attachments are re-initialized on update.

[mbostock]

Seems like we forgot to call watchAll…

await attachmentWatcher.watchAll();