Resolve name when named imp is behind wild imps (scala#21888)

When a named import (such as `import bug.util.List`) is defined before
two clashing wildcard imports (`import bug.util.*; import java.util.*`)
the name "List" should resolve to it, rather than a resolution error
being emitted.

This was due to the fact that `findRefRecur` didn't return the
precedence at which it found that import, `checkImportAlternatives` used
the `prevPrec` to `checkNewOrShadowed`.  Now we check against the entire
`foundResult`, allowing an early named import to be picked over later
wildcard imports.

Fixes scala#18529
(Replaces scala#21871)

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -268,6 +268,12 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           // special cases: definitions beat imports, and named imports beat
           // wildcard imports, provided both are in contexts with same scope
           found
+        else if newPrec == WildImport && ctx.outersIterator.exists: ctx =>
+          ctx.isImportContext && namedImportRef(ctx.importInfo.uncheckedNN).exists
+        then
+          // Don't let two ambiguous wildcard imports rule over
+          // a winning named import. See pos/i18529.
+          found
         else
           if !scala2pkg && !previous.isError && !found.isError then
             fail(AmbiguousReference(name, newPrec, prevPrec, prevCtx,

tests/pos/i18529/JCode1.java

@@ -0,0 +1,9 @@
+package bug.code;
+
+import bug.util.List;
+import bug.util.*;
+import java.util.*;
+
+public class JCode1 {
+    public void m1(List<Integer> xs) { return; }
+}

tests/pos/i18529/JCode2.java

@@ -0,0 +1,9 @@
+package bug.code;
+
+import bug.util.*;
+import bug.util.List;
+import java.util.*;
+
+public class JCode2 {
+    public void m1(List<Integer> xs) { return; }
+}

tests/pos/i18529/List.java

@@ -0,0 +1,3 @@
+package bug.util;
+
+public final class List<E> {}

tests/pos/i18529/SCode1.scala

@@ -0,0 +1,9 @@
+package bug.code
+
+import bug.util.List
+import bug.util.*
+import java.util.*
+
+class SCode1 {
+  def work(xs: List[Int]): Unit = {}
+}

tests/pos/i18529/SCode2.scala

@@ -0,0 +1,9 @@
+package bug.code
+
+import bug.util.*
+import bug.util.List
+import java.util.*
+
+class SCode2 {
+  def work(xs: List[Int]): Unit = {}
+}

tests/pos/i18529/Test.scala

@@ -0,0 +1 @@
+class Test