[mdalikadar]

Description
Adds Windows support to SignalTrait, as discussed in #10589. Without PCNTL, registerSignals() now installs a console control handler through sapi_windows_set_ctrl_handler(). It is reported to the command as SIGINT (2), because the SIG* constants come from PCNTL and are not available on Windows. A command can then stop gracefully on Ctrl+C or Ctrl+Break through shouldTerminate(), onInterruption() or a mapped method, as it does on Unix.

• unregisterSignals() removes the handler.
• getSignalName() no longer touches the SIG* constants without PCNTL, so getProcessState() works there.
• withSignalsBlocked() stays a no-op on Windows, which is documented.
• The native function sits behind a small protected wrapper so tests can replace it. The new tests run on any OS.

Refs #10589

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide