[GR-75880] Support Native Image JFR emergency dumps on Windows

[graalvmbot]

Adds Native Image support for JFR emergency dumps on Windows.

Native Image already supports writing regular JFR recordings on Windows, but out-of-memory emergency dumps were still unavailable because the emergency-dump implementation was tied to POSIX directory and file handling. This PR makes emergency dumping an OS-independent feature with small platform-specific adapters.

Implementation overview:

• Introduces AbstractJfrEmergencyDumpSupport for the common emergency-dump flow: dump path handling, repository fallback, emergency chunk creation, chunk filename validation/sorting, dump file assembly, and lifecycle test hooks.
• Refactors PosixJfrEmergencyDumpSupport to use the shared base while keeping POSIX-specific repository scanning, openat-based file opening, and path-buffer handling local to the POSIX implementation.
• Adds WindowsJfrEmergencyDumpSupport, using Win32 APIs for repository enumeration, file opening, file attributes, system time, path conversion, and cleanup.
• Extends the Windows native header bindings needed by the implementation.
• Updates JFR emergency dump tests so the same behavioral coverage can run on both POSIX and Windows, including repository fallback, support lifecycle, emergency dump contents, metadata-only dumps, constant-pool data, and non-ASCII path handling.
• Enables the JFR image demo on Windows and updates the Native Image JFR documentation to list Windows emergency dumps as supported.

Reviewer notes:

• The shared base intentionally contains the JFR/HotSpot-derived emergency-dump algorithm; the platform classes are responsible only for OS-specific path, directory, and file operations.
• Emergency repository chunks now use timestamp-style names with retry suffixes instead of a single fixed emergency_chunk.jfr, so repeated fallback chunk creation does not depend on replacing the same file.
• The companion graal-enterprise PR updates the JDK checksum metadata required by the new Windows support.