Change EnumEntry extension method to use XElement.

EnumEntry extends XElement, but currently the extension method is
attached to XTypeElement. Thus, the extension method can only be
called from XTypeElement instances, which isn't very useful since
that will always return `false`.

Test: ./gradlew :room:r-c-p:test
Change-Id: I6a629bf85d10b9bbf7c78629a2ddd66e14882e7a
diff --git a/room/room-compiler-processing/src/main/java/androidx/room/compiler/processing/XEnumEntry.kt b/room/room-compiler-processing/src/main/java/androidx/room/compiler/processing/XEnumEntry.kt
index 0006ad5..fa74017 100644
--- a/room/room-compiler-processing/src/main/java/androidx/room/compiler/processing/XEnumEntry.kt
+++ b/room/room-compiler-processing/src/main/java/androidx/room/compiler/processing/XEnumEntry.kt
@@ -33,7 +33,7 @@
     val enumTypeElement: XEnumTypeElement
 }
 
-fun XTypeElement.isEnumEntry(): Boolean {
+fun XElement.isEnumEntry(): Boolean {
     contract {
         returns(true) implies (this@isEnumEntry is XEnumEntry)
     }