[Swift5][Swift6] support "x-enum-descriptions"

[tsutsuken]

Added support for x-enum-descriptions in swift5 and swift6.

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@jgavris (2017/07) @ehyche (2017/08) @Edubits (2017/09) @jaz-ah (2017/09) @4brunu (2019/11) @dydus0x14 (2023/06)

[tsutsuken]

It looks like the CI step “Run Swift6 tests” is failing in the portion shown below; however, based on the error details, the failure seems unrelated to this PR.
Please advise if you’d like me to take any follow-up actions.
Thank you.

	Test Suite SwaggerClientTests.xctest started
APIHelperTests
    ✓ testConvertBoolToString (0.004 seconds)
    ✓ testMapValuesToQueryItems (0.004 seconds)
    ✓ testRejectNil (0.001 seconds)
    ✓ testRejectNilHeaders (0.001 seconds)
PetAPITests
    ✓ test1CreatePet (0.377 seconds)
    ✓ test2GetPet (0.075 seconds)
    ✓ test3UploadFile (0.084 seconds)
    ✓ test4DeletePet (0.073 seconds)
StoreAPITests
    ✓ test1PlaceOrder (0.077 seconds)
    ✗ test2GetOrder, failed: caught error: "error(404, Optional(53 bytes), Optional(<NSHTTPURLResponse: 0x60000048c0e0> { URL: https://petstore.swagger.io:443/v2/store/order/1000 } { Status Code: 404, Headers {
    ✓ test3DeleteOrder (0.074 seconds)
UserAPITests
    ✓ test1CreateUser (0.085 seconds)
    ✗ test2GetUser, failed: caught error: "error(404, Optional(52 bytes), Optional(<NSHTTPURLResponse: 0x600000498da0> { URL: https://petstore.swagger.io:443/v2/user/[email protected] } { Status Code: 404, Headers {
    ✓ test3DeleteUser (0.092 seconds)
    ✓ testLogin (0.071 seconds)
    ✓ testLogout (0.079 seconds)

[4brunu]

Let me try to close and reopen this PR to restart CI.

[tsutsuken]

@4brunu
Thank you. It’s still failing.
I’ll try closing and reopening this PR to re-trigger CI.

[4brunu]

CI Failure does seem to be related to this PR.

[4brunu]

Thanks for the PR 👍

[tsutsuken]

Thanks for your review!