RFR: 8372528: Unify atomic exchange and compare exchange

[Axel Boldt-Christmas]

AtomicAccess::xchg is only required to support `4` bytes and `sizeof(intptr_t)` size.
This restriction added a lot of extra logic to the Atomic implementation because
we have a set of features we must support (including compare exchange) for `1`, `4` and `8` byte atomics on all platforms. We have some checks for unsupported `8` byte compare exchange (`VM_Version::supports_cx8()`), but the Atomic class does not try to handle these for generating its supported functions. On such a platform we would more than likely get a linking error.

I propose we change requirement for exchange to `1`, `4` and `8` bytes to achieve parity with compare exchange. Initially by implementing exchange via the `AtomicAccess::XchgUsingCmpxch`. And have follow up RFEs for each applicable platform where we specialize `AtomicAccess::PlatformXchg<1>`.

This enhancement both simplifies the Atomic implementation and provides exchange capabilities for types like `bool` and enums represented by a byte.

_It is a little unclear how we deal with `VM_Version::supports_cx8()`. Its existence makes it impossible to use `compare_exchange` on `int64_t` in general code. Currently the `Atomic` implementation assumes that `exchange` can always be used on `8` byte integers (at least going by the gtest). Even though `AtomicAccess` only specifies `4` bytes and the platform size. This PR changes this to `1`, `4` and `8` bytes. But not sure if the previous behaviour / implicit requirements is an oversight a similar property to `VM_Version::supports_cx8()` should apply here for `exchange`._

* Testing
  * Extended gtest / (no other users of Atomic byte with exchange exists.
  * GHA
  * Running Tier 1-5 on Oracle supported platforms

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Commit messages:
 - Unify atomic exchange and compare exchange

Changes: https://git.openjdk.org/jdk/pull/28498/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28498&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372528
  Stats: 250 lines in 15 files changed: 108 ins; 113 del; 29 mod
  Patch: https://git.openjdk.org/jdk/pull/28498.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28498/head:pull/28498

PR: https://git.openjdk.org/jdk/pull/28498