[kotlin-client] Vert.x: Fix enum class name template for default operation parameters

[okarmazin]

This change brings the class name construction in line with the other Kotlin client generators.

Fixes #22503

As described in the issue, the Vert.X template didn't construct the enum class name correctly, leading to invalid code being generated.

Changed

{{{defaultValue}}}

to

{{#isEnum}}{{enumName}}{{operationIdCamelCase}}.{{enumDefaultValue}}{{/isEnum}}{{^isEnum}}{{{defaultValue}}}{{/isEnum}}

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[wing328]

thanks for the pr. can you please share a spec to reproduce the issue?

[okarmazin]

Sure, I'll paste the test case from the followup PR #22506 which leads to both bugs. Any spec with a defaulted enum operation parameter will exhibit this one.

Please note: This was discovered while running tests for #22506 and the fix in this PR is covered by its tests. I would have lumped both fixes in a single PR, but wanted to maintain good hygiene.

This bug is ultimately the result of the shotgun-surgery code smell present in the Kotlin client codebase. There is a large amount of code duplication among the mustache templates and tests either don't exist, or test for a single client. Because of this the Vert.x mustache template was overlooked during previous sweeping changes to the enum class name construction process.

DRY is too often thrown around as a cargo-cultish buzzword, but some drying of the Kotlin templates might be warranted here. Or maybe a policy to ensure global changes are tested for all clients, catching omissions like this.

{
  "openapi": "3.0.0",
  "info": {
    "title": "Document API",
    "version": "2025-11-25"
  },
"paths": {
  "/documents": {
    "get": {
      "tags": [
        "Document"
      ],
      "summary": "Download Document",
      "operationId": "document-download",
      "parameters": [
        {
          "name": "disposition",
          "in": "query",
          "description": "The disposition of the file.",
          "required": false,
          "deprecated": false,
          "schema": {
            "type": "string",
            "default": "inline",
            "enum": [
              "attachment",
              "inline"
            ]
          }
        }
      ],
        "responses": {
          "200": {
            "description": "File content",
            "content": {
              "application/pdf": {
                "schema": {
                  "type": "string",
                  "format": "binary"
                }
              }
            }
          }
        }
      }
    }
  }
}