[Contribution Idea] "Preserve Primary type" option for wild pokémon

[foxoftheasterisk]

Is your idea a new setting, a change to an existing setting, or something else? Please describe clearly:
This would be a new setting that could be applied to wild pokémon. (It could also be extended to apply to trainers.)

Its effect would be to ensure that the original pokémon's primary type would be present in the randomized pokémon. (For example, an Oddish (Grass-Poison) might randomize into a Tangela (pure Grass), an Exeggcute (Grass-Psychic), or a Paras (Bug-Grass).)

It would be compatible any of the randomization styles (full, area 1-to-1, global 1-to-1). It would be compatible with "Similar strength" (with some fudging, as is done on type themed trainers). It would not be compatible with Catch em All mode or type themed areas.

What problem would your contribution solve? Please describe:
This would preserve a lot of the type theming of the original games, including "soft" type theming such as having bug and grass types in a forest.

It would especially lead to less strange water encounters, as nearly all pokémon encountered when Surfing, fishing, and Diving are primary Water types.

However it would also allow some variety of types, as only the primary type is preserved, allowing for unexpected dual-types.

Additional context:
To be honest, I'm going to implement this for my personal use either way. What's in question is whether I put in the extra effort to make it fully compatible with all settings/use cases (instead of just the ones I use).

I understand that I am expected to implement this change myself in the randomizer's codebase: [X]