Add a convenience method to Symbol to "resugar" fields

val and var members of classes are split into getter/setter and field
symbols. However, we can't call `defString` on any of these and see
what existed in source code.

Example:

```
scala> class X { protected var x: Int = 0 }
defined class X

scala> val xField = typeOf[X].member(TermName("x "))
xField: $r.intp.global.Symbol = variable x

scala> xField.defString
res10: String = private[this] var x: Int

scala> xField.getterIn(xField.owner).defString
res11: String = protected def x: Int

scala> xField.setterIn(xField.owner).defString
res12: String = protected def x_=(x$1: Int): Unit
```

This commit introduces a new method on `Symbol` that pieces together
the information from these symbols to create an artificial symbol
that has the `defString` we're after:

```
scala> xField.sugaredSymbolOrSelf.defString
res14: String = protected var x: Int
```

1 files changed, 13 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index 2e3449588b..4bdb8e6da8 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -500,6 +500,19 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
       case _            => new StubTermSymbol(this, name.toTermName, missingMessage)
     }
 
+    /** Given a field, construct a term symbol that represents the source construct that gave rise the the field */
+    def sugaredSymbolOrSelf = {
+      val getter = getterIn(owner)
+      if (getter == NoSymbol) {
+        this
+      } else {
+        val result = owner.newValue(getter.name.toTermName, newFlags = getter.flags & ~Flags.METHOD).setPrivateWithin(getter.privateWithin).setInfo(getter.info.resultType)
+        val setter = setterIn(owner)
+        if (setter != NoSymbol) result.setFlag(Flags.MUTABLE)
+        result
+      }
+    }
+
 // ----- locking and unlocking ------------------------------------------------------
 
     // True if the symbol is unlocked.