fix: handle discriminators in experimental parser

[mrlubos]

Closes https://github.com/hey-api/openapi-ts/issues/993

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🦋 Changeset detected

Latest commit: ff3aa4ac58068671d2b9eedbd7528eb4f9969386

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ------------------- | ----- | | @hey-api/openapi-ts | Patch |

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Codecov Report

Attention: Patch coverage is 52.88136% with 139 lines in your changes missing coverage. Please review.

Project coverage is 67.56%. Comparing base (04c88dd) to head (ff3aa4a). Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ages/openapi-ts/src/openApi/3.0.x/parser/schema.ts	9.48%	105 Missing :warning:
...ages/openapi-ts/src/openApi/3.1.x/parser/schema.ts	76.06%	28 Missing :warning:
.../openapi-ts/src/plugins/@hey-api/schemas/plugin.ts	50.00%	3 Missing :warning:
...enapi-ts/src/openApi/shared/utils/discriminator.ts	85.71%	2 Missing :warning:
...kages/openapi-ts/src/openApi/3.0.x/parser/index.ts	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1267 +/- ## ========================================== - Coverage 67.63% 67.56% -0.08% ========================================== Files 132 133 +1 Lines 19684 19841 +157 Branches 1775 1784 +9 ========================================== + Hits 13314 13405 +91 - Misses 6366 6432 +66 Partials 4 4 ``` | [Flag](https://app.codecov.io/gh/hey-api/openapi-ts/pull/1267/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=hey-api) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/hey-api/openapi-ts/pull/1267/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=hey-api) | `67.56% <52.88%> (-0.08%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=hey-api#carryforward-flags-in-the-pull-request-comment) to find out more.

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