FIR: Fix false positive INAPPLICABLE_INFIX_MODIFIER

compiler/fir/analysis-tests/testData/resolve/diagnostics/infixFunctions.kt

@@ -10,4 +10,15 @@ infix class A
 
 infix typealias B = A
 
-infix val x = 1
+infix val x = 1
+
+class C {
+    infix fun good(x: Int) {}
+    infix fun Int.goodAsWell(x: Int) {}
+
+    <!INAPPLICABLE_INFIX_MODIFIER!>infix fun Int.foo(x: Int, y: Int) {}<!>
+
+    <!INAPPLICABLE_INFIX_MODIFIER!>infix fun Int.bar() {}<!>
+
+    <!INAPPLICABLE_INFIX_MODIFIER!>infix fun baz(x: Int, y: Int) {}<!>
+}

compiler/fir/analysis-tests/testData/resolve/diagnostics/infixFunctions.txt

@@ -16,3 +16,24 @@ FILE: infixFunctions.kt
     public final typealias B = R|A|
     public final val x: R|kotlin/Int| = Int(1)
         public get(): R|kotlin/Int|
+    public final class C : R|kotlin/Any| {
+        public constructor(): R|C| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final infix fun good(x: R|kotlin/Int|): R|kotlin/Unit| {
+        }
+
+        public final infix fun R|kotlin/Int|.goodAsWell(x: R|kotlin/Int|): R|kotlin/Unit| {
+        }
+
+        public final infix fun R|kotlin/Int|.foo(x: R|kotlin/Int|, y: R|kotlin/Int|): R|kotlin/Unit| {
+        }
+
+        public final infix fun R|kotlin/Int|.bar(): R|kotlin/Unit| {
+        }
+
+        public final infix fun baz(x: R|kotlin/Int|, y: R|kotlin/Int|): R|kotlin/Unit| {
+        }
+
+    }

compiler/fir/analysis-tests/testData/resolve/fromBuilder/typeParameters.kt

@@ -1,7 +1,7 @@
 interface List<out T : Any> {
     operator fun get(index: Int): T
 
-    <!INAPPLICABLE_INFIX_MODIFIER!>infix fun concat(other: List<T>): List<T><!>
+    infix fun concat(other: List<T>): List<T>
 }
 
 typealias StringList = List<out String>