FIR: use SyntheticPropertySymbol & synthetic scope instead of FirAccessorSymbol

Before this commit, we used FirAccessorSymbol to emulate synthetic properties.
These symbols were generated in Java use-site scope.
Now, we use synthetic scope instead which is above MemberScopeTowerLevel.
This is more performance-friendly and does not require override matching.
However, accessor symbols should be used in situation when Java accessor
overrides Kotlin property which is broken in this commit
(that's why MapEntry test is corrupted here).
Also, we should not create synthetics for pure Kotlin accessors
(that's why javaAccessorConversion test is corrupted here).

compiler/fir/tree/src/org/jetbrains/kotlin/fir/symbols/SyntheticSymbol.kt

@@ -5,4 +5,9 @@
 
 package org.jetbrains.kotlin.fir.symbols
 
-interface SyntheticSymbol
+interface SyntheticSymbol
+
+interface AccessorSymbol : SyntheticSymbol {
+    val callableId: CallableId // it's an id of related property (synthetic or not)
+    val accessorId: CallableId // it's an id of accessor function
+}

compiler/fir/tree/src/org/jetbrains/kotlin/fir/symbols/impl/FirFunctionSymbol.kt

@@ -6,8 +6,8 @@
 package org.jetbrains.kotlin.fir.symbols.impl
 
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.symbols.AccessorSymbol
 import org.jetbrains.kotlin.fir.symbols.CallableId
-import org.jetbrains.kotlin.fir.symbols.SyntheticSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
@@ -35,8 +35,8 @@ class FirConstructorSymbol(
 
 class FirAccessorSymbol(
     callableId: CallableId,
-    val accessorId: CallableId
-) : FirFunctionSymbol<FirSimpleFunction>(callableId), SyntheticSymbol
+    override val accessorId: CallableId
+) : FirFunctionSymbol<FirSimpleFunction>(callableId), AccessorSymbol
 
 // ------------------------ unnamed ------------------------