Unavailable Java members from mapping J2K in stdlib

[vmishenev]

interface MyCharSequence: CharSequence

This has chars() and codePoints() members that are absent in https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-char-sequence/ (and in the new documentation too) since they come from mapping (see https://kotlinlang.org/docs/java-interop.html#mapped-types) Java to Kotlin/Kotlin to Java.

The actual DRIs of chars() and codePoints() have thekotlin package so after fixing #3529 they lead to non-existent https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-char-sequence/chars.html and https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-char-sequence/code-points.html

This is also relevant to #2879 (e.g. Dokka generates .../kotlin-stdlib/kotlin.collections/-collection/parallel-stream.html that is a 404-page)

Possible expected behaviour

• StdLib documentation should generate such pages
• DRI should lead to Javadoc documentation, in this case, https://docs.oracle.com/javase/8/docs/api/java/lang/CharSequence.html#chars-- and https://docs.oracle.com/javase/8/docs/api/java/lang/CharSequence.html#codePoints--