formula_creator: move initial CLI values into constructor

[abitrolly]

Sets initial values for formula fields from CLI params.

Another refactoring for code clarity to keep #16238 minimal.

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[MikeMcQuaid]

Nice work. Looking good so far. Some suggested extensions.

[MikeMcQuaid]

Liking the progress, nice work!

[abitrolly]

@MikeMcQuaid should be good now.

[MikeMcQuaid]

Thanks again @abitrolly, really great work here. Think we're almost there 🤞🏻

[abitrolly]

@MikeMcQuaid done.

[MikeMcQuaid]

Great work again, thanks @abitrolly!