Give special precedence to & and | type operators

Unlike others (which here follow Scala 2 precedence), they should follow the
term-level precedence.

Author: Blaisorblade

compiler/src/dotty/tools/dotc/parsing/package.scala

@@ -2,7 +2,7 @@ package dotty.tools.dotc
 
 import util.Chars._
 import core.Names.Name
-import core.StdNames.nme
+import core.StdNames.{nme,tpnme}
 import core.NameOps._
 
 package object parsing {
@@ -11,7 +11,12 @@ package object parsing {
     if (operator eq nme.ERROR) -1
     /* SLS 3.2.10 (https://www.scala-lang.org/files/archive/spec/2.13/03-types.html#infix-types):
      * all infix types have the same precedence */
-    else if (isType) minInfixPrec
+    else if (isType) {
+      if (operator == tpnme.raw.AMP || operator == tpnme.raw.BAR)
+        precedence(operator, false)
+      else
+        minInfixPrec
+    }
     else {
       val firstCh = operator.firstPart.head
       if (isScalaLetter(firstCh)) 1

compiler/test-resources/type-printer/infix

@@ -21,13 +21,13 @@ def foo: (Int &: String) && Boolean
 scala> def foo: Int &: (Boolean && String) = ???
 def foo: Int &: (Boolean && String)
 scala> def foo: (Int & String) &: Boolean = ???
-def foo: (Int & String) &: Boolean
+def foo: Int & String &: Boolean
 scala> def foo: Int & (Boolean &: String) = ???
 def foo: Int & (Boolean &: String)
 scala> def foo: (Int &: String) & Boolean = ???
 def foo: (Int &: String) & Boolean
 scala> def foo: Int &: (Boolean & String) = ???
-def foo: Int &: (Boolean & String)
+def foo: Int &: Boolean & String
 scala> import scala.annotation.showAsInfix
 scala> @scala.annotation.showAsInfix class Mappy[T,U]
 // defined class Mappy
@@ -44,18 +44,18 @@ def foo: ||[Int, Boolean]
 scala> def foo: Int && Boolean & String = ???
 def foo: Int && Boolean & String
 scala> def foo: (Int && Boolean) & String = ???
-def foo: Int && Boolean & String
+def foo: (Int && Boolean) & String
 scala> def foo: Int && (Boolean & String) = ???
-def foo: Int && (Boolean & String)
+def foo: Int && Boolean & String
 scala> def foo: Int && (Boolean with String) = ???
-def foo: Int && (Boolean & String)
-scala> def foo: (Int && Boolean) with String = ???
 def foo: Int && Boolean & String
+scala> def foo: (Int && Boolean) with String = ???
+def foo: (Int && Boolean) & String
 scala> def foo: Int && Boolean with String = ???
-def foo: Int && (Boolean & String)
+def foo: Int && Boolean & String
 scala> def foo: Int && Boolean | String = ???
 def foo: Int && Boolean | String
 scala> def foo: Int && (Boolean | String) = ???
-def foo: Int && (Boolean | String)
-scala> def foo: (Int && Boolean) | String = ???
 def foo: Int && Boolean | String
+scala> def foo: (Int && Boolean) | String = ???
+def foo: (Int && Boolean) | String