related to #15455

Backup service is no longer writing to its metadata on startup in a way that it blocks the startup. Previously we had:

• an async write very early (async but still blocking)
• a sync write for each window that opens

This showed up as largest block in profiles for me when looking for main process and seems to result in a significant reduction from todays exploration build:

Tracing the remaining sync fs operations, we still do, they seem not to be significant (profile attached below):

• configureCommandlineSwitchesSync - we read argv.json on startup to support runtime flags very early and we must set the flags before app.on("ready") so imho this is fine
• getUntitledWorkspacesSync - we check for untitled workspaces with a readDirSync call since we always restore untitled workspaces
• statSync - we still check paths to open with a stat call to know if the file exists and what type it is (folder vs file)

These remaining ones are not in an async context and I wonder how far we want to push it. I think changing the remaining ones would require us to change to async window opening which would probably be a larger undertaking.

Attached profile, I was searching for sync in the profile to find every location (77 in total, mainly from node.js require calls):
prof-ZKVq5BB7.main.cpuprofile.zip

And found some more that can actually be fixed, either by removing or since they are in an async context:

• perf - make resolving untitled workspaces async (#16381) #160591
• debt - avoid sync fs in registerWorkspaceBackup #160593
• perf - avoid redundant statSync when opening files via macOS dock #160594

Ended up making opening windows async, and thus was able to remove the sync fs calls. We still need to read argv.json on startup to configure Electron switches, but the rest is all async now, esp. the initially mentioned statSync calls to validate paths to open.

Thanks @bpasero - This issue almost turned 6 🍰 and yielded good speed up