remove ByteSize and WordSize classes

This is placeholder to have some discussion about how we could remove ByteSize and WordSize.

Here is a comment from sizes.hpp that explains what these classes are for:

// The following two classes are used to represent 'sizes' and 'offsets' in the VM;
// they serve as 'unit' types. ByteSize is used for sizes measured in bytes, while
// WordSize is used for sizes measured in machine words (i.e., 32bit or 64bit words
// depending on platform).

One problem is that it introduces quite some verbosity to code like assembler code because in order to get a byte-sized offset you have to call in_bytes, e.g.:

  add(cache, cache, in_bytes(ConstantPoolCache::base_offset()));

The other downsize is the fact that a number of methods have a "in_bytes" suffix, e.g.:

  static int pool_holder_offset_in_bytes() { return offset_of(ConstantPool, _pool_holder); }

And ugly example of how word-sizes are used is:

  static int size(int length) { return align_object_size(header_size() + length * in_words(ConstantPoolCacheEntry::size())); }

which is then called as:

    assert(in_words(ConstantPoolCacheEntry::size()) == 4, "adjust shift below");

Too many in_words calls for my taste; it makes the code difficult to read.