Because `public JvmTypeExtensionVisitor` was removed, a new place for `const val PLATFORM_TYPE_ID`
is required. It is logical to place it as a some kind of constant for Km node;
however, because it is platform-specific, there is a need for an empty
`KmFlexibleTypeUpperBound.Companion` in metadata common sources
and `public val KmFlexibleTypeUpperBound.Companion.PLATFORM_TYPE_ID`
extension in kotlin-metadata-jvm sources.
See also: KT-63156
Leonid Startsev
cc343d7fb3