KT-9547: private package member can conflict only with the members

declared in the same file.
Cleanup OverloadUtil stuff.
Update testData.

compiler/testData/diagnostics/tests/redeclarations/RedeclarationInMultiFile.kt

@@ -1,9 +1,9 @@
 // FILE: a.kt
-val <!REDECLARATION, REDECLARATION!>a<!> : Int = 1
+val <!REDECLARATION!>a<!> : Int = 1
 <!CONFLICTING_OVERLOADS!>fun f()<!> {
 }
 
 // FILE: b.kt
-val <!REDECLARATION, REDECLARATION!>a<!> : Int = 1
+val <!REDECLARATION!>a<!> : Int = 1
 <!CONFLICTING_OVERLOADS!>fun f()<!> {
 }

compiler/testData/diagnostics/tests/redeclarations/RedeclaringPrivateToFile.kt

@@ -0,0 +1,40 @@
+// FILE: a.kt
+package a
+
+interface A
+interface B : A
+
+private fun validFun() {}
+
+private val validProp = 1
+
+<!CONFLICTING_OVERLOADS!>private fun invalidFun1()<!> {}
+<!CONFLICTING_OVERLOADS!>private fun invalidFun1()<!> {}
+
+<!CONFLICTING_OVERLOADS!>private fun invalidFun2()<!> {}
+<!CONFLICTING_OVERLOADS!>public fun invalidFun2()<!> {}
+
+<!CONFLICTING_OVERLOADS!>public fun invalidFun3()<!> {}
+
+<!CONFLICTING_OVERLOADS!>private fun invalidFun4()<!> {}
+<!CONFLICTING_OVERLOADS, CONFLICTING_OVERLOADS!>public fun invalidFun4()<!> {}
+
+public fun validFun2(a: A) = a
+public fun validFun2(b: B) = b
+
+// FILE: b.kt
+package a
+
+private fun validFun() {}
+
+private val validProp = 1
+
+<!CONFLICTING_OVERLOADS!>internal fun invalidFun3()<!> {}
+<!CONFLICTING_OVERLOADS!>internal fun invalidFun4()<!> {}
+
+// FILE: c.kt
+package a
+
+public fun validFun() {}
+
+public val validProp = 1

compiler/testData/diagnostics/tests/redeclarations/RedeclaringPrivateToFile.txt

@@ -0,0 +1,33 @@
+package
+
+package a {
+    private val validProp: kotlin.Int = 1
+    private val validProp: kotlin.Int = 1
+    public val validProp: kotlin.Int = 1
+    private fun invalidFun1(): kotlin.Unit
+    private fun invalidFun1(): kotlin.Unit
+    private fun invalidFun2(): kotlin.Unit
+    public fun invalidFun2(): kotlin.Unit
+    internal fun invalidFun3(): kotlin.Unit
+    public fun invalidFun3(): kotlin.Unit
+    internal fun invalidFun4(): kotlin.Unit
+    private fun invalidFun4(): kotlin.Unit
+    public fun invalidFun4(): kotlin.Unit
+    private fun validFun(): kotlin.Unit
+    private fun validFun(): kotlin.Unit
+    public fun validFun(): kotlin.Unit
+    public fun validFun2(/*0*/ a: a.A): a.A
+    public fun validFun2(/*0*/ b: a.B): a.B
+
+    public interface A {
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    public interface B : a.A {
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}

compiler/testData/diagnostics/tests/redeclarations/kt470.kt

@@ -1,11 +1,11 @@
-val <!REDECLARATION, REDECLARATION!>a<!> : Int = 1
-val <!REDECLARATION, REDECLARATION!>a<!> : Int = 1
-val <!REDECLARATION, REDECLARATION!>a<!> : Int = 1
+val <!REDECLARATION!>a<!> : Int = 1
+val <!REDECLARATION!>a<!> : Int = 1
+val <!REDECLARATION!>a<!> : Int = 1
 
-val <!REDECLARATION, REDECLARATION!>b<!> : Int = 1
-val <!REDECLARATION, REDECLARATION!>b<!> : Int = 1
-val <!REDECLARATION, REDECLARATION!>b<!> : Int = 1
-val <!REDECLARATION, REDECLARATION!>b<!> : Int = 1
+val <!REDECLARATION!>b<!> : Int = 1
+val <!REDECLARATION!>b<!> : Int = 1
+val <!REDECLARATION!>b<!> : Int = 1
+val <!REDECLARATION!>b<!> : Int = 1
 
 <!CONFLICTING_OVERLOADS!>fun foo()<!> {} // and here too
 <!CONFLICTING_OVERLOADS!>fun foo()<!> {} // and here