[FIR] Introduce different synthetic origins for FIR declarations

This is needed to be able to precisely distinguish different synthetic
  declarations (like fields for delegates and functions for data classes)
  in fir2ir

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirDeclarationOrigin.kt

@@ -23,7 +23,17 @@ sealed class FirDeclarationOrigin(
         object Library : Java("Java(Library)")
     }
 
-    object Synthetic : FirDeclarationOrigin()
+    sealed class Synthetic : FirDeclarationOrigin() {
+        object DataClassMember : Synthetic()
+        object ValueClassMember : Synthetic()
+        object JavaProperty : Synthetic()
+        object DelegateField : Synthetic()
+        object PluginFile : Synthetic()
+        object Error : Synthetic()
+        object TypeAliasConstructor : Synthetic()
+        object FakeFunction : Synthetic()
+        object ForwardDeclaration : Synthetic()
+    }
     object DynamicScope : FirDeclarationOrigin()
     object SamConstructor : FirDeclarationOrigin()
     object Enhancement : FirDeclarationOrigin()

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/synthetic/FirSyntheticProperty.kt

@@ -51,7 +51,7 @@ class FirSyntheticProperty(
         get() = null
 
     override val origin: FirDeclarationOrigin
-        get() = FirDeclarationOrigin.Synthetic
+        get() = FirDeclarationOrigin.Synthetic.JavaProperty
 
     override val initializer: FirExpression?
         get() = null

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/synthetic/FirSyntheticPropertyAccessor.kt

@@ -34,7 +34,7 @@ class FirSyntheticPropertyAccessor(
         get() = delegate.moduleData
 
     override val origin: FirDeclarationOrigin
-        get() = FirDeclarationOrigin.Synthetic
+        get() = FirDeclarationOrigin.Synthetic.JavaProperty
 
     override val returnTypeRef: FirTypeRef
         get() = delegate.returnTypeRef

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/utils/FirDeclarationUtil.kt

@@ -34,7 +34,7 @@ inline val FirDeclaration.isFromLibrary: Boolean
 inline val FirDeclaration.isPrecompiled: Boolean
     get() = origin == FirDeclarationOrigin.Precompiled
 inline val FirDeclaration.isSynthetic: Boolean
-    get() = origin == FirDeclarationOrigin.Synthetic
+    get() = origin is FirDeclarationOrigin.Synthetic
 
 // NB: This function checks transitive localness. That is,
 // if a declaration `isNonLocal`, then its parent also `isNonLocal`.