Make isStatic force less.

It's called in a lot of maps and forcing presents a risk of stale symbol
errors. So we should force the minimum possible.

Author: odersky

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -562,7 +562,7 @@ object SymDenotations {
 
     /** Is this denotation static (i.e. with no outer instance)? */
     final def isStatic(implicit ctx: Context) =
-      (if (maybeOwner eq NoSymbol) isRoot else maybeOwner.isStaticOwner) ||
+      (if (maybeOwner eq NoSymbol) isRoot else maybeOwner.originDenotation.isStaticOwner) ||
         myFlags.is(JavaStatic)
 
     /** Is this a package class or module class that defines static symbols? */

compiler/src/dotty/tools/dotc/core/Symbols.scala

@@ -435,6 +435,10 @@ object Symbols {
       newd
     }
 
+    /** The original denotation of this symbol, without forcing anything */
+    final def originDenotation: SymDenotation =
+      lastDenot.initial
+
     /** The last known denotation of this symbol, without going through `current` */
     final def lastKnownDenotation: SymDenotation =
       lastDenot

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

@@ -1,4 +1,5 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package printing
 
 import core._