Move newline handling down into parser.

This lets us make it a grammar feature and not a lexer trick.
Newlines are explicitly ignored in some parts of the grammar. This
lets, for example, things like "|" ignore the newline when used as
an operator, but not when used as a parameter delimiter in a block
argument.

test/class/newline_after_static.wren

@@ -0,0 +1,6 @@
+class Foo {
+  static // expect error
+  method {} // expect error
+}
+
+// The second error is cascaded.