Get ProtoOutputStream size without compressing it

The current implementation of the ProtoOutputStream compresses the
buffer in order to return its correct size.

For some use cases the compression is too expensive and it is more
useful to have a faster but overestimated size to a precise but slower
one.

This implementation adds a `getRawSize` method which returns the buffer
size without compressing it. If the buffer has already been compressed
the returned size is the same as the one from the `getSize`. If the
buffer is not yet compressed the size may diverge.

This implementation will be used to support a ring buffer for window
transitions on the Window Manager.

Bug: 123535780
Test: Check the getSize method from the EncodedBuffer and the getRawSize
from the ProtoOutputStream.
Change-Id: Ied24742a14b76980afdf6d6d22d67ade15ba7aad