[K/N][build] Change MetaVersion to inline class from enum

Support meta versions strings other than pre-defined. All enum entries
were left for source-level compatibility.

dependencies/kotlin-build-gradle-plugin/src/VersionGenerator.kt

@@ -81,9 +81,9 @@ open class VersionGenerator : DefaultTask() {
     @Input
     open val buildNumber = project.findProperty("build.number")?.toString()
 
-    @Input
+    @get:Input
     open val meta = (project.findProperty("konanMetaVersion") as? String
-        ?: kotlinNativeProperties["konanMetaVersion"])?.let { MetaVersion.valueOf(it.toString().toUpperCase()) }
+        ?: kotlinNativeProperties["konanMetaVersion"])?.let { MetaVersion.findAppropriate(it.toString()) }
         ?: MetaVersion.DEV
 
     fun defaultVersionFileLocation() {