Avoid using vararg in API

Both because it complicates function calls, especially when vararg is not the last argument. Also there is possible performance impact because of array re-wrapping in kotlin.

No files, tests, or entry points are named. Start by locating the public Kotlin API declarations that use vararg and their call sites, then determine the affected surface and how compatibility should be evaluated. Done means the agreed API no longer uses the targeted vararg patterns and relevant callers or tests remain valid.

Written by the indexing model from the issue text.