[kotlin-multiplatform] Fix enum value issues in path or query

[grEvenX]

This commit fixes an issue where enums are used as a value in either path or query params due to relying on string casting.
With this change, enum values are requested by using .value instead.

Solves #18236

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[grEvenX]

Pinging the technical committee for review; @jimschubert @dr4ke616 @karismann @Zomzog @andrewemery @4brunu @yutaka0m @stefankoppier

[4brunu]

Looks good to me 👍