RFR: JDK-8175036 All API docs should be built for HTML 5

[Magnus Ihse Bursie]

We should switch all uses of the javadoc tool to generate documentation 
in HTML 5, using the -html5 option.

Bug: https://bugs.openjdk.java.net/browse/JDK-8175036
Patch inline:
diff --git a/make/Javadoc.gmk b/make/Javadoc.gmk
--- a/make/Javadoc.gmk
+++ b/make/Javadoc.gmk
@@ -84,7 +84,7 @@
  # The initial set of options for javadoc
  JAVADOC_OPTIONS := -XDignore.symbol.file=true -use -keywords 
-notimestamp \
      -serialwarn -encoding ISO-8859-1 -breakiterator -splitIndex 
--system none \
-    --expand-requires transitive
+    -html5 --expand-requires transitive

  # Should we add DRAFT stamps to the generated javadoc?
  ifeq ($(VERSION_IS_GA), true)

/Magnus