[Kotlin] add BigDecimal, BigInteger support

[codymikol]

this allows the kotlin client generator to support
BigDecimal values

This was originally created by @kuFEAR in their own branch, but a PR wasn't made into this project.
I hope you don't mind me making the PR for you, I happen to need this for my own project.

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Kotlin

@jimschubert (2017/09) ❤️, @dr4ke616 (2018/08) @karismann (2019/03) @Zomzog (2019/04) @andrewemery (2019/10) @4brunu (2019/11) @yutaka0m (2020/03)

[4brunu]

Hey, thanks for your contribution 👍
One question, does kotlin client from OpenAPI generates the types BigDecimal and BigInteger?
Thanks

[kuFEAR]

it works if you add typeMappings.set(mapOf("double" to "BigDecimal")) in configuration

[4brunu]

If I'm understanding what you are saying, it's possible to change the typeMappings?
I didn't knew this feature.

But by default it doesn't generate BigDecimal from what I understood.

If by default the generator doesn't generate BigDecimal, I'm not sure if this makes sense to add this adapters to the default configuration.
Because if you use a custom types, you can add custom adapters via Serializer.moshiBuilder.add(...)

Also this PR adds the BigDecimal and BigInteger adapters, but it doesn't add them to Serializer.moshiBuilder.

I'm not sure whats the right move here, let's here the other technical committee members.

[codymikol]

If I'm understanding what you are saying, it's possible to change the typeMappings?
I didn't knew this feature.

But by default it doesn't generate BigDecimal from what I understood.

If by default the generator doesn't generate BigDecimal, I'm not sure if this makes sense to add this adapters to the default configuration.
Because if you use a custom types, you can add custom adapters via Serializer.moshiBuilder.add(...)

Also this PR adds the BigDecimal and BigInteger adapters, but it doesn't add them to Serializer.moshiBuilder.

I'm not sure whats the right move here, let's here the other technical committee members.

That was actually supposed to be in there, I let it slip through after rebasing, just pushed it in now. Thanks for catching that!

[wing328]

@codymikol can you please resolve the merge conflicts when you've time?

[codymikol]

@codymikol can you please resolve the merge conflicts when you've time?

I'll take a look tomorrow

[codymikol]

@wing328 sorry for the delay

EDIT: Actually it looks like the CI is failing with some unrelated error, is this a problem for everyone?

[wing328]

Updated the samples via 093d63b. Let's see if all the tests pass.

[codymikol]

Thanks wing 👍