[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/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/CommonCompilerArguments.kt

@@ -818,7 +818,7 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
                 )
             }
             put(AnalysisFlags.optIn, useExperimentalFqNames + optIn?.toList().orEmpty())
-            put(AnalysisFlags.skipExpectedActualDeclarationChecker, expectActualLinker)
+            put(AnalysisFlags.skipExpectedActualDeclarationChecker, expectActualLinker || metadataKlib) // TODO (KT-61136): drop `expectActualLinker` later, after the appropriate changes in the Gradle plugin
             put(AnalysisFlags.explicitApiVersion, apiVersion != null)
             put(AnalysisFlags.allowResultReturnType, allowResultReturnType)
             ExplicitApiMode.fromString(explicitApi)?.also { put(AnalysisFlags.explicitApiMode, it) } ?: collector.report(