[Object] Modify OwningBinary's interface to separate inspection from ownership.

[Object] Modify OwningBinary's interface to separate inspection from ownership.

The getBinary and getBuffer method now return ordinary pointers of appropriate
const-ness. Ownership is transferred by calling takeBinary(), which returns a
pair of the Binary and a MemoryBuffer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221003 91177308-0d34-0410-b5e6-96231b3b80d8