fix: #2802 - let SnapshotSource reuse self-generated snapshot

[cknaap]

Description

If SnapshotSource detects a snapshot generated by our own SnapshotGenerator, it does not re-generate it.

Related issues

Fixes #2802.

Testing

See 2 new unit tests in the PR.

FirelyTeam Checklist

• Update the title of the PR to be succinct and less than 50 characters
• Mark the PR with the label breaking change when this PR introduces breaking changes

[ewoutkramer]

I do not understand why #2802 is considered a bug. When you set the setting "ForceRegenerateSnapshots" to true, it will re-generate the snapshots, no matter what. This is the documented behaviour of this option:

Force expansion of all external profiles, disregarding any existing snapshot components.
If enabled, the snapshot generator will re-generate the snapshot components of all the core resource and datatype profiles
as well as of all other referenced external profiles.
Re-generated snapshots are annotated to prevent duplicate re-generation (assuming the provided resource resolver uses caching).
If disabled (default), then the snapshot generator relies on existing snapshot components, if they exist.

This PR does not look like a fix, but a behavioural change. The "ForceRegenerateSnapshot" used to always regenerate the snapshot, now it will only renegerate it if it was not created by us. That's a breaking change that we should not make in a non-major version.

Why don't you just set ForceRegenerateSnapshot to false instead? This will create a new snapshot if there is none, or if the snapshot is not ours.

[ewoutkramer]

Design discussion will be continued on issue #2802.

[Kasdejong]

I think this PR is overall an improvement now. From what I've read this is what we're going with, so I'll pull it

[Kasdejong]

I will also deprecate the setting for good measure, because it seems as though right now it does not do anything. In fact, setting it to false while there is no snapshot will just produce no snapshot now :)

[mmsmits]

As Ewout says in #2802 this will surely result in regressions. We shouldn't change this.

[mmsmits]

This still needs to be done:

We should obsolete it and introduce a more explicit setting. Basically there are only two cases:
- Add a snapshot if there is none or use whatever is there (new behaviour)
- Regenerate snapshot once to ensure it is "ours" (and/or at least updated to the lastest version) (current default behaviour)