Fix tests: "infix modifier required" and "operator modifier required" errors

idea/testData/intentions/removeUnnecessaryParentheses/necessaryParentheses5.kt

@@ -1,7 +1,7 @@
 // IS_APPLICABLE: false
 interface Foo {
-    fun get(x : Any) : Foo
-    fun plus(x : Any) : Foo
+    operator fun get(x : Any) : Foo
+    operator fun plus(x : Any) : Foo
 }
 fun foo(x: Foo) {
     <caret>(x + x)[x]

idea/testData/intentions/removeUnnecessaryParentheses/unnecessaryParentheses3.kt

@@ -1,5 +1,5 @@
 interface Foo {
-    fun get(x : Any) : Foo
+    operator fun get(x : Any) : Foo
 }
 fun foo(x: Foo) {
     <caret>(x[x])[x]

idea/testData/intentions/removeUnnecessaryParentheses/unnecessaryParentheses3.kt.after

@@ -1,5 +1,5 @@
 interface Foo {
-    fun get(x : Any) : Foo
+    operator fun get(x : Any) : Foo
 }
 fun foo(x: Foo) {
     x[x][x]

idea/testData/intentions/removeUnnecessaryParentheses/unnecessaryParentheses4.kt

@@ -1,6 +1,6 @@
 interface Foo {
-    fun inc() : Foo
-    fun not() : Foo
+    operator fun inc() : Foo
+    operator fun not() : Foo
 }
 fun foo(x: Foo) {
     !(<caret>x.inc())

idea/testData/intentions/removeUnnecessaryParentheses/unnecessaryParentheses4.kt.after

@@ -1,6 +1,6 @@
 interface Foo {
-    fun inc() : Foo
-    fun not() : Foo
+    operator fun inc() : Foo
+    operator fun not() : Foo
 }
 fun foo(x: Foo) {
     !x.inc()

idea/testData/intentions/removeUnnecessaryParentheses/unnecessaryParentheses8.kt

@@ -1,5 +1,5 @@
 class C() {
-    fun get(i: Int) = i + 1
+    operator fun get(i: Int) = i + 1
 
     // KT-4513: Unnecessary parenthesis around 'this'
     val foo = (this<caret>)[41]

idea/testData/intentions/removeUnnecessaryParentheses/unnecessaryParentheses8.kt.after

@@ -1,5 +1,5 @@
 class C() {
-    fun get(i: Int) = i + 1
+    operator fun get(i: Int) = i + 1
 
     // KT-4513: Unnecessary parenthesis around 'this'
     val foo = this[41]