[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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