chore: mark AnyRef::eq and AnyRef::ne as infix instead of special casing when emitting the warning (#23252)

Closes #23251

<img width="825" alt="Screenshot 2025-05-23 at 16 01 54"
src="https://github.com/user-attachments/assets/3844700b-3efe-4ca6-85f0-ce4b9e6e5ac7"
/>

Author: hamzaremmal

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -428,8 +428,8 @@ class Definitions {
   @tu lazy val AnyRefAlias: TypeSymbol = enterAliasType(tpnme.AnyRef, ObjectType)
   def AnyRefType: TypeRef = AnyRefAlias.typeRef
 
-    @tu lazy val Object_eq: TermSymbol = enterMethod(ObjectClass, nme.eq, methOfAnyRef(BooleanType), Final)
-    @tu lazy val Object_ne: TermSymbol = enterMethod(ObjectClass, nme.ne, methOfAnyRef(BooleanType), Final)
+    @tu lazy val Object_eq: TermSymbol = enterMethod(ObjectClass, nme.eq, methOfAnyRef(BooleanType), Final | Infix)
+    @tu lazy val Object_ne: TermSymbol = enterMethod(ObjectClass, nme.ne, methOfAnyRef(BooleanType), Final | Infix)
     @tu lazy val Object_synchronized: TermSymbol = enterPolyMethod(ObjectClass, nme.synchronized_, 1,
         pt => MethodType(List(pt.paramRefs(0)), pt.paramRefs(0)), Final)
     @tu lazy val Object_clone: TermSymbol = enterMethod(ObjectClass, nme.clone_, MethodType(Nil, ObjectType), Protected)
@@ -2042,10 +2042,6 @@ class Definitions {
   def hasProblematicGetClass(className: Name): Boolean =
     HasProblematicGetClass.contains(className)
 
-  /** Is synthesized symbol with alphanumeric name allowed to be used as an infix operator? */
-  def isInfix(sym: Symbol)(using Context): Boolean =
-    (sym eq Object_eq) || (sym eq Object_ne)
-
   @tu lazy val assumedTransparentNames: Map[Name, Set[Symbol]] =
     // add these for now, until we had a chance to retrofit 2.13 stdlib
     // we should do a more through sweep through it then.

compiler/src/dotty/tools/dotc/core/SymUtils.scala

@@ -359,7 +359,6 @@ class SymUtils:
     /** Is symbol assumed or declared as an infix symbol? */
     def isDeclaredInfix(using Context): Boolean =
       self.is(Infix)
-      || defn.isInfix(self)
       || self.name.isUnapplyName
         && self.owner.is(Module)
         && self.owner.linkedClass.is(Case)