[KLIB] Use -Xmetadata-klib to produce metadata KLIBs

With this change a new `-Xmetadata-klib` CLI flag becomes the
preferable way to instruct K2MetadataCompiler to produce metadata
KLIBs. The old `-Xexpect-actual-linker` flag still works for
K2MetadataCompiler, but that would last just for a short transition
period until the necessary changes are made in the Gradle plugin.

The K2NativeCompiler does not work anymore with `-Xexpect-actual-linker`
and respects only the `-Xmetadata-klib` flag. This is not an
issue since the Gradle plugin anyway supplies both flags for Native
metadata compilations.

^KT-61136

compiler/tests/org/jetbrains/kotlin/jvm/compiler/AbstractCompileKotlinAgainstCustomBinariesTest.kt

@@ -686,14 +686,14 @@ abstract class AbstractCompileKotlinAgainstCustomBinariesTest : AbstractKotlinCo
     fun testAnonymousObjectTypeMetadataKlib() {
         val klibLibrary = compileCommonLibrary(
             libraryName = "library",
-            listOf("-Xexpect-actual-linker"),
+            listOf("-Xmetadata-klib"),
         )
         compileKotlin(
             "anonymousObjectTypeMetadata.kt",
             tmpdir,
             listOf(klibLibrary),
             K2MetadataCompiler(),
-            listOf("-Xexpect-actual-linker")
+            listOf("-Xmetadata-klib")
         )
     }