RFR: CODETOOLS-7903291: jcstress: Optimize jcstress trap handling

[Aleksey Shipilev]

Currently, jcstress does `jcstress_sink(...)` method to let early NP-checks for field accesses persist. But this is not required: we can just store the value in the local variable, and the NP-checking effects would persist. This saves cycles calling the method in interpeter mode.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jcstress/pull/121/files
 Webrev: https://webrevs.openjdk.org/?repo=jcstress&pr=121&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903291
  Stats: 14 lines in 1 file changed: 0 ins; 6 del; 8 mod
  Patch: https://git.openjdk.org/jcstress/pull/121.diff
  Fetch: git fetch https://git.openjdk.org/jcstress pull/121/head:pull/121

PR: https://git.openjdk.org/jcstress/pull/121