8358183: [JVMCI] crash accessing nmethod::jvmci_name in CodeCache::aggregate

[bulasevich]

This change addresses an intermittent crash in CompileBroker::print_heapinfo() when accessing JVMCI metadata after a CodeBlob::purge().

The issue is a regression after:

• JDK-8343789: JVMCI metadata was moved from nmethod into a separate blob.
• JDK-8352112: CodeBlob::purge() was updated to set _mutable_data to blob_end().

The change zeroes out _mutable_data_size, _relocation_size, and _metadata_size in purge() so that after purge jvmci_data_size() returns 0 and CompileBroker::print_heapinfo() won’t touch an invalid _metadata.

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Progress

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Issue

• JDK-8358183: [JVMCI] crash accessing nmethod::jvmci_name in CodeCache::aggregate (Bug - P3)

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