RFR: 8253278: Refactor/cleanup oopDesc::*_klass_addr

[Aleksey Shipilev]

Right now this one has the comment mentioning CMS:

Klass** oopDesc::klass_addr(HeapWord* mem) {
  // Only used internally and with CMS and will not work with
  // UseCompressedOops
  assert(!UseCompressedClassPointers, "only supported with uncompressed klass pointers");
  ByteSize offset = byte_offset_of(oopDesc, _metadata._klass);
  return (Klass**) (((char*)mem) + in_bytes(offset));
}

But that is not true, it is used on the generic paths.

The rest are the snowballing changes:
 - in `load_klass_raw` and `set_klass`: `compressed_klass_addr` and `klass_addr` are used where the direct access to
   `_metadata` can be done, avoiding these methods
 - the leftover use is in `set_klass_release`, where we can simplify things by inlining `_addr` methods directly
 - `CHECK_SET_KLASS` macro seems too much ceremony for just two asserts

Note that new code uses the universal `klass_offset_in_bytes`, that is technically `offset_of(..., _metadata._klass)`.
This is different from the previous code, but it matches what other code is doing -- it trusts that both
`_metadata._klass` and `_metadata._compressed_klass` are on the same offsets. I thought to add a very paranoid assert
there, but decided not to.

Testing: Linux x86_64 fastdebug tier1

-------------

Commit messages:
 - Whitespace
 - Simplify it even more
 - 8253278: Refactor/cleanup oopDesc::*_klass_addr

Changes: https://git.openjdk.java.net/jdk/pull/221/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=221&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253278
  Stats: 46 lines in 3 files changed: 1 ins; 34 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/221.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/221/head:pull/221

PR: https://git.openjdk.java.net/jdk/pull/221