Ideas of enhancements for persist function

[AkariiinMKII]

Here's the situation I met when using persist function in manifest.
There is an app, whose config file needs to be persisted but:

• The config file won't be generated before launching.
• The app is not compatible with empty config file (may cause app broken).

Additionally, all persist values without existing items found are treated as folder name in current version.
Of course we can use custom scripts to solve this, however, it will be nice if we are able to declare properties like persist_as_file and force_persist in persist function, and it is supposed to work when installing, uninstalling and updating:

Furtherly, some apps may break file links that persist cannot work with them, could we add a backup field in manifest with functions to backup and restore items instead of persisting, which is also implemented by custom scripts.

[niheaven]

See #3248 for persistence rework, but that’s outdated and needs some updating. Does that logic fit your need?

[AkariiinMKII]

Yes, it perfectly meets my demands if add a new field force.

[niheaven]

Okay, then I'll carefully cherrypick the PR's commit and update it, please wait for it.