Flush local history before shutdown when connected to a remote

[bpasero]

Because the remote connection can drop at any time, it is somewhat dangerous to flush local history only on shutdown.

Refs: https://github.com/github/codespaces/issues/7228

[bpasero]

@jkeech can you verify this using insiders with Codespaces? Thanks!

[bpasero]

Verification:

• open timeline for a file
• save the file and notice a local history entry
• edit the entry, give it a different name
• disconnect from the remote
• connect again and ensure the history entry name is still there

[jkeech]

Verified on Insiders in Codespaces. Thanks for the fix! ❤️