FIR checker: report unresolved reference in imports

Compared to FE1.0, instead of using UNRESOLVED_REFERENCE, a new
UNRESOLVED_IMPORT diagnostic is introduced. This is so that we can use a
different positioning strategy to highlight the last part of the import
if the entire import is passed.

Also, this change fixed some incorrectly rejected imports in FIR. Such
cases are covered the newly added test file staticFunAndPropertyImport.kt

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/declarations/ImplicitReceiverUtils.kt

@@ -196,6 +196,6 @@ fun ImplicitReceiverValue<*>.asTowerDataElement(): FirTowerDataElement =
 fun FirScope.asTowerDataElement(isLocal: Boolean): FirTowerDataElement =
     FirTowerDataElement(this, implicitReceiver = null, isLocal)
 
-private fun FirClass.staticScope(sessionHolder: SessionHolder) =
+fun FirClass.staticScope(sessionHolder: SessionHolder) =
     scopeProvider.getStaticScope(this, sessionHolder.session, sessionHolder.scopeSession)
 typealias FirLocalScopes = PersistentList<FirLocalScope>

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/diagnostics/ConeDiagnostics.kt

@@ -198,6 +198,11 @@ class ConeImportFromSingleton(val name: Name) : ConeDiagnostic {
 
 open class ConeUnsupported(override val reason: String, val source: KtSourceElement? = null) : ConeDiagnostic
 
+class ConeUnresolvedParentInImport(val parentClassId: ClassId) : ConeDiagnostic {
+    override val reason: String
+        get() = "unresolved import"
+}
+
 class ConeUnsupportedDynamicType : ConeUnsupported("Dynamic types are not supported in this context")
 
 class ConeDeprecated(