Generate equals()/hashCode(): Fix hashCode() implementation

#KT-11638 Fixed

idea/testData/codeInsight/generate/equalsWithHashCode/arrays.kt.after

@@ -22,8 +22,8 @@ class A(val n: IntArray, val s: Array<String>) {
 
     override fun hashCode(): Int{
         var result = Arrays.hashCode(n)
-        result += 31 * result + Arrays.hashCode(s)
-        result += 31 * result + f.hashCode()
+        result = 31 * result + Arrays.hashCode(s)
+        result = 31 * result + f.hashCode()
         return result
     }
 }

idea/testData/codeInsight/generate/equalsWithHashCode/multipleVars.kt.after

@@ -20,8 +20,8 @@ class A(val n: Int, val s: String) {
 
     override fun hashCode(): Int{
         var result = n
-        result += 31 * result + s.hashCode()
-        result += 31 * result + f.hashCode()
+        result = 31 * result + s.hashCode()
+        result = 31 * result + f.hashCode()
         return result
     }
 }

idea/testData/codeInsight/generate/equalsWithHashCode/multipleVarsNullable.kt.after

@@ -20,8 +20,8 @@ class A(val n: Int?, val s: String) {
 
     override fun hashCode(): Int{
         var result = n ?: 0
-        result += 31 * result + s.hashCode()
-        result += 31 * result + (f?.hashCode() ?: 0)
+        result = 31 * result + s.hashCode()
+        result = 31 * result + (f?.hashCode() ?: 0)
         return result
     }
 }

idea/testData/codeInsight/generate/equalsWithHashCode/multipleVarsWithSuperClass.kt.after

@@ -26,9 +26,9 @@ class A(val n: Int, val s: String) : X() {
 
     override fun hashCode(): Int{
         var result = super.hashCode()
-        result += 31 * result + n
-        result += 31 * result + s.hashCode()
-        result += 31 * result + f.hashCode()
+        result = 31 * result + n
+        result = 31 * result + s.hashCode()
+        result = 31 * result + f.hashCode()
         return result
     }
 }

idea/testData/codeInsight/generate/equalsWithHashCode/nameClash.kt.after

@@ -17,7 +17,7 @@ class A(val result: Int, val s: String) {
 
     override fun hashCode(): Int{
         var result1 = result
-        result1 += 31 * result1 + s.hashCode()
+        result1 = 31 * result1 + s.hashCode()
         return result1
     }
 }

idea/testData/codeInsight/generate/equalsWithHashCode/nullableArrays.kt.after

@@ -22,8 +22,8 @@ class A(val n: IntArray?, val s: Array<String>?) {
 
     override fun hashCode(): Int{
         var result = n?.let { Arrays.hashCode(it) } ?: 0
-        result += 31 * result + (s?.let { Arrays.hashCode(it) } ?: 0)
-        result += 31 * result + f.hashCode()
+        result = 31 * result + (s?.let { Arrays.hashCode(it) } ?: 0)
+        result = 31 * result + f.hashCode()
         return result
     }
 }

idea/testData/codeInsight/generate/equalsWithHashCode/singleVarWithJavaSuperClass.kt.after

@@ -17,7 +17,7 @@ class A(val n: Int) : X() {
 
     override fun hashCode(): Int{
         var result = super.hashCode()
-        result += 31 * result + n
+        result = 31 * result + n
         return result
     }
 }

idea/testData/codeInsight/generate/equalsWithHashCode/singleVarWithSuperClass.kt.after

@@ -22,7 +22,7 @@ class A(val n: Int) : X() {
 
     override fun hashCode(): Int{
         var result = super.hashCode()
-        result += 31 * result + n
+        result = 31 * result + n
         return result
     }
 }