Fix #7634: Use (x: C) instead of C(x) for printing singleton types

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -229,7 +229,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
   }.close
 
   def toTextSingleton(tp: SingletonType): Text =
-    toTextLocal(tp.underlying) ~ "(" ~ toTextRef(tp) ~ ")"
+    "(" ~ toTextRef(tp) ~ " : " ~ toTextGlobal(tp.underlying) ~ ")"
 
   protected def paramsText(tp: LambdaType): Text = {
     def paramText(name: Name, tp: Type) = toText(name) ~ toTextRHS(tp)

tests/neg/cannot-reduce-inline-match.check

@@ -4,6 +4,6 @@
   |  cannot reduce inline match with
   |   scrutinee:  {
   |    "f"
-  |  } : String("f")
+  |  } : ("f" : String)
   |   patterns :  case _:Int
   | This location contains code that was inlined from cannot-reduce-inline-match.scala:3

tests/neg/exports.check

@@ -52,4 +52,4 @@
    |               ^
    |               Double definition:
    |               val bar: Bar in class Baz at line 45 and
-   |               final def bar: => => Bar(Baz.this.bar.baz.bar)(Baz.this.bar.bar) in class Baz at line 46
+   |               final def bar: => (Baz.this.bar.bar : => (Baz.this.bar.baz.bar : Bar)) in class Baz at line 46

tests/neg/inline-error-pos.check

@@ -4,6 +4,6 @@
   |          cannot reduce inline match with
   |           scrutinee:  {
   |            2
-  |          } : Int(2)
+  |          } : (2 : Int)
   |           patterns :  case 1
   | This location contains code that was inlined from inline-error-pos.scala:3