Refactor MPP versioning

- Use 'null' as indicator of non-MPP version. Consequently, remove
useless 'isMpp' method, and lift all methods to extensions (to be able
to call them on nullable 'facetSettings.mppVersion')

- Change semantics of extensions to check for exact equality rather than
for "at least specified version"

- Deprecate old MPP-versioning in favour of 'facetSettings.mppVersion'

Original commit: 958a7d9315

jps/jps-common/src/org/jetbrains/kotlin/config/KotlinFacetSettings.kt

@@ -134,6 +134,7 @@ enum class KotlinModuleKind {
     SOURCE_SET_HOLDER,
     COMPILATION_AND_SOURCE_SET_HOLDER;
 
+    @Deprecated("Use KotlinFacetSettings.mppVersion.isNewMpp")
     val isNewMPP: Boolean
         get() = this != DEFAULT
 }
@@ -141,18 +142,18 @@ enum class KotlinModuleKind {
 enum class KotlinMultiplatformVersion(val version: Int) {
     M1(1), // the first implementation of MPP. Aka 1.2.0 MPP
     M2(2), // the "New" MPP. Aka 1.3.0 MPP
-    M3(3); // the "Hierarchical" MPP.
+    M3(3) // the "Hierarchical" MPP.
-
-    val isMPPModule: Boolean
-        get() = version >= 1
-
-    val isNewMPP: Boolean
-        get() = version >= 2
-
-    val isHMPP: Boolean
-        get() = version >= 3
 }
 
+val KotlinMultiplatformVersion?.isOldMpp: Boolean
+    get() = this == KotlinMultiplatformVersion.M1
+
+val KotlinMultiplatformVersion?.isNewMPP: Boolean
+    get() = this == KotlinMultiplatformVersion.M2
+
+val KotlinMultiplatformVersion?.isHmpp: Boolean
+    get() = this == KotlinMultiplatformVersion.M3
+
 data class ExternalSystemTestTask(val testName: String, val externalSystemProjectId: String, val targetName: String?) {
 
     fun toStringRepresentation() = "$testName|$externalSystemProjectId|$targetName"

jps/jps-common/src/org/jetbrains/kotlin/config/facetSerialization.kt

@@ -331,7 +331,7 @@ private fun KotlinFacetSettings.writeLatestConfig(element: Element) {
         element.setAttribute("externalProjectId", externalProjectId)
     }
     if (isHmppEnabled) {
-        element.setAttribute("isHmppProject", isHmppEnabled.toString())
+        element.setAttribute("isHmppProject", mppVersion.isHmpp.toString())
     }
     if (externalSystemTestTasks.isNotEmpty()) {
         saveElementsList(