[Commonizer] Provide union of forwardDeclarations as common dependencies

^KT-52050 Verification Pending

The issue described in KT-52050 happened, because forwardDeclarations
were not carried into next commonization steps. For commonization
it is fair to choose the union of all modules forwardDeclarations
as common dependency (instead of a union), since we can assume that
all those forward declarations will be provided.

native/commonizer-api/test/org/jetbrains/kotlin/commonizer/CommonizeNativeDistributionTest.kt

@@ -103,6 +103,23 @@ class CommonizeNativeDistributionTest {
         )
     }
 
+    @Test
+    fun `commonize - linux macos - linux macos mingw`() {
+        val unixTarget = CommonizerTarget(LINUX_X64, MACOS_X64)
+        val nativeTarget = CommonizerTarget(MINGW_X64, LINUX_X64, MACOS_X64)
+        CliCommonizer(this::class.java.classLoader).commonizeNativeDistribution(
+            konanHome = konanHome,
+            outputTargets = setOf(unixTarget, nativeTarget),
+            outputDirectory = temporaryOutputDirectory.root,
+            logLevel = CommonizerLogLevel.Info
+        )
+
+        assertTrue(
+            resolveCommonizedDirectory(temporaryOutputDirectory.root, nativeTarget).isDirectory,
+            "Expected directory for $nativeTarget"
+        )
+    }
+
     @Test
     fun `commonize - no outputTargets specified`() {
         CliCommonizer(this::class.java.classLoader).commonizeNativeDistribution(