* Model crashNow's intentional crash as a trap under scan-build

The null-pointer store is the deliberate never-returning crash, but
clang scan-build reports a null dereference. Under __clang_analyzer__,
replace it with __builtin_trap() - the analyzer understands the trap as
a halt and explores no false path past it; the real build keeps the
store.

* Add JFR event types for reference chains

Introduces the ReferenceChainEvent/ReferenceChainAbandonedEvent payloads
(event.h), their JFR metadata (jfrMetadata.*), and the FlightRecorder
emission paths that serialize chain events into JFR recording buffers,
including the constant-pool handling for per-hop edge labels. Emission
is pull-style: profiler.cpp snapshots events and hands them to
FlightRecorder; this layer does not depend on the tracker itself.

* Keep chain events inside the recording buffer; keep truncated labels

Review findings on the JFR plumbing layer:

- MAX_REFERENCE_CHAIN_EVENT_HOPS was a fixed 4096, permitting a ~438 KB
  worst-case event (near-limit edge labels) against a ~61 KB recording
  buffer - the reservation flushed first but the margin underflowed, so
  the write ran past the buffer (debug assert, release corruption). The
  cap is now derived from RECORDING_BUFFER_LIMIT minus the event's fixed
  fields, divided by the per-hop worst case, so a full-cap event always
  fits.
- Truncation dropped ALL edge labels: the label count was gated on
  _edges.size() == emitted_size, which only holds for untruncated
  chains. Labels align with the chain's leaf-first element order, so
  truncation now emits the first emitted_size labels and loses only the
  root-side ones.
- ObjectLivenessEvent::leak_tag is default-initialized to 0 so any
  construction path that forgets to set it serializes a defined
  untagged value (flush_table() overwrites it from the entry, which
  track() zeroes at insert).

Moves the JFR round-trip and arguments parsing unit tests into this
layer (they test exactly this code), rewrites the round-trip test to
construct events directly instead of through the tracker, and adds
byte-level boundary tests: oversize-chain truncation with label
preservation, the size-prefix invariant, and the default leak tag.

* Drop transient and stale line-number references from comments

Uncommitted plan documents, rotted .cpp:NNN line references, and a
nonexistent j9WallClock.cpp path replaced with symbol references that
stay valid as the code moves.

* Address review: merge chain hops, trim comments, drop doc/jira refs

- ReferenceChainEvent carries one vector of ReferenceChainHop
  (klass id + retention-edge label) instead of two parallel vectors
- Compress the sub-option floor/ceiling rationale and the provisional
  default constant comments to one concise statement each
- Drop design-doc and Jira references from code comments; revert the
  unrelated LineNumberTable comment rewrite

* Make comments layer-local: no references to later stack layers

The event/argument comments named collector classes, methods and files
that do not exist at this layer of the stack; describe the contracts
without those forward references instead.

* Drop a later-layer class name from the arguments test comment

* Clamp reference-chain edge labels to the reserved cap when writing

* Reuse reservation constants and drop edge_labels stack array in recordReferenceChain