RFR: 8289710: Move Suspend/Resume classes out of os.hpp [v3]

[Ioi Lam]

> Please review this simple change that only renames a few classes and moved some code around. No functional changes.
> 
> The following classes are used only sparingly. They should be moved to a new header file share/runtime/suspend.hpp to minimize the size of os.hpp
> 
> - SuspendedThreadTaskContext
> - SuspendedThreadTask
> - SuspendResume
> 
> I didn't move the OS-specific implementation to a new file -- the POSIX implementation is currently inside [signals_posix.cpp](https://github.com/openjdk/jdk/blob/df063f7db18a40ea7325fe608b3206a6dff812c1/src/hotspot/os/posix/signals_posix.cpp#L1790) mixed with other signal handling code, so it doesn't seem a good idea to move out just the code for the above 3 classes.
> 
> The only other implementation is in os_windows.cpp. I could move the code to suspend_windows.cpp, but I don't feel very motivated unless someone insists.

Ioi Lam has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into 8289710-move-suspend-classes-out-of-os-hpp
 - moved SuspendResume class to os/posix directory
 - 8289710: Move Suspend/Resume classes out of os.hpp

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9371/files
  - new: https://git.openjdk.org/jdk/pull/9371/files/8265ecb2..46ab65b8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9371&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9371&range=01-02

  Stats: 12133 lines in 385 files changed: 5838 ins; 2311 del; 3984 mod
  Patch: https://git.openjdk.org/jdk/pull/9371.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9371/head:pull/9371

PR: https://git.openjdk.org/jdk/pull/9371