Improve support of custom equals in inline classes

- Ensure that typed equals parameter's type is a star projection of
  corresponding inline class

- Make possible to declare typed equals that returns 'Nothing'

- Forbid type parameters in typed equals operator declaration

^KT-54909 fixed
^KT-54910 fixed

compiler/testData/codegen/box/inlineClasses/inlineOverInlineWithCustomEquals.kt

@@ -6,7 +6,7 @@
 
 OPTIONAL_JVM_INLINE_ANNOTATION
 value class A(val x: Int) {
-    fun equals(other: A) = true
+    operator fun equals(other: A) = true
 }
 
 class C
@@ -20,13 +20,13 @@ value class B2(val x: A?)
 
 OPTIONAL_JVM_INLINE_ANNOTATION
 value class D1(val x: C) {
-    fun equals(other: D1) = true
+    operator fun equals(other: D1) = true
 }
 
 
 OPTIONAL_JVM_INLINE_ANNOTATION
 value class D2(val x: C?) {
-    fun equals(other: D2) = true
+    operator fun equals(other: D2) = true
 }
 
 OPTIONAL_JVM_INLINE_ANNOTATION