Fix the return type of java generator

The return type of java generator is fixed to root element. And we
cannot have more than one root elemnt.
As the number of root elements is limited, the Cpp generator is also
changed.

Bug: 112397063
Test: m -j
Test: cd out/host/linux-x86/testcases/xsdc-cpp-test/x86_64 &&
      ./xsdc-cpp-tests

Change-Id: I2db662d644b4222f1a7495b4be9725314325e8f7
13 files changed
tree: 7f974494741c6955a51a28b5cb6ad3e6e7f282b8
  1. build/
  2. src/
  3. tests/
  4. Android.bp
  5. MANIFEST.MF