SI-3368 CDATA gets a Node

XML Parser uses `scala.xml.PCData`.

A compiler flag `-Yxml:coalescing`, analogous to
`DocumentBuilderFactory.setCoalescing`, turns `PCData`
nodes into `Text` nodes and coalesces sibling text nodes.

This change also fixes parse errors such as rejecting a
sequence of CDATA sections.

A sequence of "top level" nodes are not coalesced.

```
scala> <a><b/>start<![CDATA[hi & bye]]><c/>world<d/>stuff<![CDATA[red & black]]></a>
res0: scala.xml.Elem = <a><b/>start<![CDATA[hi & bye]]><c/>world<d/>stuff<![CDATA[red & black]]></a>

scala> :replay -Yxml:coalescing
Replaying: <a><b/>start<![CDATA[hi & bye]]><c/>world<d/>stuff<![CDATA[red & black]]></a>
res0: scala.xml.Elem = <a><b/>starthi &amp; bye<c/>world<d/>stuffred &amp; black</a>
```

1 files changed, 18 insertions, 0 deletions

diff --git a/test/files/run/t3368.scala b/test/files/run/t3368.scala
new file mode 100644
index 0000000000..aaf34b43fb
--- /dev/null
+++ b/test/files/run/t3368.scala
@@ -0,0 +1,18 @@
+
+import scala.tools.partest.ParserTest
+
+
+object Test extends ParserTest {
+
+  override def code = """
+  trait X {
+    // error: in XML literal: name expected, but char '!' cannot start a name
+    def x = <![CDATA[hi & bye]]> <![CDATA[red & black]]>
+  }
+  trait Y {
+    def y = <a><b/>start<![CDATA[hi & bye]]><c/>world<d/>stuff<![CDATA[red & black]]></a>
+  }
+  """
+
+  override def extraSettings = s"${super.extraSettings} -Yxml:coalescing"
+}