Backport "Avoid repetitions in name hints" to LTS (#20998)

Backports #19975 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

compiler/src/dotty/tools/dotc/reporting/DidYouMean.scala

@@ -149,7 +149,7 @@ object DidYouMean:
       if d != 0 || b.sym.is(ModuleClass) => // Avoid repeating the same name in "did you mean"
         if qualifies(b) then
           def hint(b: Binding) = prefix ++ showName(b.name, b.sym)
-          val alts = alternatives(d, rest).map(hint).take(3)
+          val alts = alternatives(d, rest).filter(_.name != b.name).map(hint).take(3).distinct
           val suffix = if alts.isEmpty then "" else alts.mkString(" or perhaps ", " or ", "?")
           s" - did you mean ${hint(b)}?$suffix"
         else

tests/neg/i19958.check

@@ -0,0 +1,8 @@
+-- [E008] Not Found Error: tests/neg/i19958.scala:1:21 -----------------------------------------------------------------
+1 |val b = new Object().unit // error
+  |        ^^^^^^^^^^^^^^^^^
+  |        value unit is not a member of Object - did you mean Object.wait?
+-- [E008] Not Found Error: tests/neg/i19958.scala:10:10 ----------------------------------------------------------------
+10 |val d = c.unit // error
+   |        ^^^^^^
+   |        value unit is not a member of C - did you mean c.blit? or perhaps c.wait?

tests/neg/i19958.scala

@@ -0,0 +1,11 @@
+val b = new Object().unit // error
+
+abstract class C:
+  def wait: Unit
+  def wait(x: Int): Unit
+  def blit: Unit
+  def blit(x: Int): Unit
+
+val c: C = ???
+val d = c.unit // error
+