Keep native frames intact under --package-names - #5

Problem

stacks --package-names abbreviate|drop (#4) promises to change only package-qualified Java frames, but it rewrote most native frames that async-profiler records inside the Java stack:

The library is the only thing that says whether run belongs to HotSpot, a JNI library or the profiler. The rewrite replaced it with so., and symbols from different libraries could merge. There were three causes:

• the collapsed key drops each frame's type;
• the profile tagged every Java-stack frame JAVA;
• the package pattern accepted libjvm. as a package.

Change

• Frame type decides. The correlator records which frames of each collapsed key async-profiler typed as Java code (Interpreted, JIT compiled, C1 compiled, Inlined). If stacks that share a key disagree about a frame, that frame counts as native.
• New frame kind. The profile tags the other frames with a new kind, JFR_NATIVE (wire value 4), and moves to schema_version 2.
  • Schema 1 profiles still read.
  • An older correlator refuses a new profile with Unsupported stack profile schema.
  • merge combines stacks with the same frame names whatever kinds its inputs gave them, and a frame any input calls native stays native.
• Only JAVA frames are rewritten. A name rule protects schema 1 profiles and backs up the kinds: a name with ::, a shared-library segment (.so., .so.6.), a leading / or [, or a space is never rewritten.
• Hidden-class lambdas. A hidden class's .0x… suffix (Foo$$Lambda.0x0000000081a16ff8.run) now stays part of the class, so drop removes its package too. Before, these frames kept their full package.
• Export. export adds a last column, java_stack_kinds (javaStackKinds in JSON Lines), holding java or native per frame. Existing columns are unchanged.
• Docs. The proto comments, OFFLINE.md and README §5 are updated. README §5 gains a table that includes a native row.

Collapsed keys and frame names are unchanged, so the default rendering still reproduces jonoffcpu-offcpu-stacks.collapsed byte for byte.

Verification

• ./gradlew spotlessCheck :jonoffcpu-correlator:check passes. The new fixtures cover:
  • the spec's frame table, for both kinds and all three modes;
  • the type-to-kind mapping, including disagreement between stacks;
  • a schema 1 profile round trip and merge;
  • refusal of the new kind in a schema 1 file and of an unknown schema;
  • identical filter totals in every mode;
  • the export column.
• Pulsar broker profile written before the fix (schema 1, name rule only):
  • Before the fix, abbreviate and drop produced 1,844 so./l.so. frame occurrences. Now there are none.
  • All 264 native frames of the full render keep their names in both modes.
  • The default and full renders are byte-identical to the old correlator's.
  • --exclude summary totals are identical in all three modes.
• Profile re-correlated from a broker capture (schema 2, with kinds):
  • The export tags 484 frame names native and 1,433 Java, with no conflicts.
  • The default render equals the collapsed file.
  • The old correlator refuses the profile with Unsupported stack profile schema.