Expand `pkg-self` scripted test to cover #2326

The previous version of `pkg-self` covered scenario where a package object
inherited directly from a class that is being modified and recompiled in
subsequent steps. The #2326 shows that name hashing fails to handle
a package object that inherits indirectly from a modified class. In that
case, name hashing fails to invalidate the source file that defines the
package object.
This commit expands `pkg-self` with a class B that inherits from modified
class `A` and makes package object inherit from B. We mark that test as
pending to show that this indeed trigger the bug in name hashing.

sbt/src/sbt-test/source-dependencies/pkg-self/changes/B.scala

@@ -1,5 +1,3 @@
-package demo
+package demo.sub
 
-object B {
-   3.y
-}
+class B extends A

sbt/src/sbt-test/source-dependencies/pkg-self/changes/C.scala

@@ -0,0 +1,5 @@
+package demo
+
+object D {
+   3.y
+}

sbt/src/sbt-test/source-dependencies/pkg-self/changes/package.scala

@@ -1,3 +1,3 @@
-package object demo extends sub.A {
+package object demo extends sub.B {
   val y = 9
 }

sbt/src/sbt-test/source-dependencies/pkg-self/pending

@@ -1,8 +1,9 @@
 # Here we have a package object (demo) that extends a class in a subpackage (demo.sub.A)
-#  demo.sub.A provides an implicit used by demo.B
+#  demo.sub.A provides an implicit used by demo.D
 $ copy-file changes/package.scala src/main/scala/demo/package.scala
 $ copy-file changes/A1.scala src/main/scala/demo/sub/A.scala
 $ copy-file changes/B.scala src/main/scala/demo/B.scala
+$ copy-file changes/C.scala src/main/scala/demo/C.scala
 > compile
 
 # When recompiling A, we delete the class files for A