[BUG][Kotlin-client] Handling default values of parameters

Created by: sjoblomj

Resolves #10865 (closed)

Different Kotlin clients currently handle default values of parameters differently; some ignore them, some use the default value. Some also generate invalid Kotlin code, such as @Header("hn1") hn1: java.math.BigDecimal = 71.0 (Double cannot be assigned to BigDecimal).

This PR attempts to make the default values of parameters consistent and without invalid code. It also tidies up the generated comments a little, which unfortunately leads to a lot of changed sample files.

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