Replace IsOriginalValue() with IsModified and fix merging and casting of default option values

[fflaten]

PR Summary

Only modify configuration options that have actually been changed when casting and merging configurations.

Option.IsOriginalValue() is marked obsolete and is replaced by a new Option.IsModified-property that enables us to fix merging of serialized PesterConfiguration.

Fix #2198

PR Checklist

• PR has meaningful title
• Summary describes changes
• PR is ready to be merged
  • If not, use the arrow next to Create Pull Request to mark it as a draft. PR can be marked Ready for review when it's ready.
• Tests are added/update (if required)
• Documentation is updated/added (if required)

[fflaten]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[fflaten]

@nohwnd:

• Thoughts on this?
• Any reason to not replace IsOriginalValue() with a getter-only property? That would let us serialize/deserialize it in PesterConfiguration-objects. We could hide it in the formats we generate if necessary. Or keep both method and property (slightly different name) if we believe someone's using the method outside Pester-runtime, which I doubt

[nohwnd]

Any reason to not replace IsOriginalValue() with a getter-only property?

I think having it not show up in the output was the only reason.

[fflaten]

Ready for review.
I could change to IsDefaultValue if you'd like to avoid mini-breaking change and keep IsOriginalValue().

[nohwnd]

IsDefaultValue seems like better name. Please put IsOriginalValue() back and mark it deprecated (with Obsolete attribute). Just to be nice about semantic versioning.

[nohwnd]

I don't see it used in open source, but let's still be nice: https://grep.app/search?q=IsOriginalValue%28%29

[fflaten]

IsDefaultValue seems like better name.

After letting the name sink in, it could confuse someone when it's false while Default and Value are equal (but modified). 😅. Naming is hard. IsModified?