[GR-67169] JFR emergency dump

[graalvmbot]

Summary:
This PR adds Native Image JFR emergency-dump support and hardens the runtime for the OOM and recovered-OOM cases exercised by it.

Main changes:

• implement the emergency-dump runtime path in SubstrateVM JFR, including the required POSIX support
• fix repository snapshot/reset handling when metadata and type-table allocations fail during OOM-sensitive paths
• keep the emergency stop path allocation-free by separating it from normal recording stop/flush behavior
• discard stale thread-local JFR and sampler state after an emergency dump so a later recording restart is safe
• add focused regression coverage for emergency dumps, recovered-OOM handling, and the layered-image interaction

Review guidance:

• the main review surface is the SubstrateVM JFR emergency path and repository/reset logic
• the last follow-up commit is only the layered-image compatibility fix after the cleanup changes

Original contribution by @roberttoyonaga .