Editor: load changes to file in the background if file already loaded

[bpasero]

Setup:

• open 2 files
• switch between them

Today:

• we go to disk each time to check if the file on disk has changed

Proposed:

• show the file instantly without going to disk
• check for the file having changed in the background

The consequences are:

• files will load instantly when opened once during the session (good)
• if the file has changed on disk (and we missed the file event when this happened) it is possible that the editor is updated later (I think that is OK)
• if the user manages to make the file dirty before this update happens, the risk of seeing a save conflict (not ideal, but this is should not be the 99% case)

Overall this optimizes performance for the 99% case and especially remote editing scenarios where resource access is potentially slow.

[bpasero]

Verify:

• prepare a setup where you have 2 tabs open (or more) and an external editor to make changes to any of the files
• switching between the files should work as before
• make changes to the file externally and verify that switching files shows the content updated (this only works if the files are not dirty in VSCode)

[WilliamStone]

In some cases user wishes keeping the opened editor content as is and not updating to new content. I think there should be a dialog to notify user of file content change and confirm whether to load changed file. The dialog is per file, and has 4 options of: Yes, No, Yes for all, and No for all, so user can
have fine grained control when needed, and no bother when not needed. And provide a command to let user manually load changed file.