[kotlin-client] ALL: Prevent HTML-escaping of operation parameter defaults

[okarmazin]

Fixes #22505

Kotlin client API templates now pass through enum defaults of operation parameters as raw values. Prevents incorrect HTML-escaping of Kotlin backticks if the default enum constant is a reserved Kotlin word.

Old output:

fun documentDownload(disposition: DispositionDocumentDownload? = DispositionDocumentDownload.`inline`) : java.io.File

Fixed output:

fun documentDownload(disposition: DispositionDocumentDownload? = DispositionDocumentDownload.`inline`) : java.io.File

New tests should cover all present and future clients that generate enum classes.

This PR builds upon #22504 and I'll rebase when that gets merged.

The GitHub diff viewer is not very good. This is a single-character change in multiple templates that replaces {{enumDefaultValue}} with {{&enumDefaultValue}}

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