feature: add support for constant values

[robertadkins]

Closes #1834

See the issue above for a description of a usecase where support for the const keyword is useful. Updated the snapshot tests to verify correct output.

[robertadkins]

Since const was added in OpenAPI v3.1 (see discussion in #1834), updating this PR to only modify the v3 parsing and tests.

[mrlubos]

@robertadkins we've decided to merge this pull request in our fork, thanks for this feature!

[kovalewvladimir]

@robertadkins we've decided to merge this pull request in our fork, thanks for this feature!

Thank you. It really works in the fork.

[mrlubos]

@kovalewvladimir are there any other issues you're running into with this package?

[lausek]

@ferdikoomen Can we get this merged please? This is such a small PR and as far as I understand it, it would enable discriminated type unions.

[mrlubos]

@lausek This package has been unmaintained for years so I guess the answer is a no. What's stopping you from using @hey-api?

[lausek]

Yet it isn't archived and the last commit was two weeks ago.

I don't want hey-api because 1) it is not compatible at all with the current state of the generated client and 2) I don't want generated code in my repo from which I only use 50% (throwOnError)

I just want a simple generated typescript client with discriminated type unions and I think that is not too much to ask for. 🥲 But yea, fork it is then.

[ferdikoomen]

Hi @lausek, @mrlubos is right, this repo is unmaintained. You really should switch to hey-api :-) I do occasionally commit a dependency/security update, but that is it.