RFR: 8318586: Explicitly handle upcall stub allocation failure [v4]

[Jorn Vernee]

> Explicitly handle UpcallStub allocation failures by terminating. We currently might try to use the returned `nullptr` which would fail sooner or later. This patch just makes the termination explicit.

Jorn Vernee has updated the pull request incrementally with three additional commits since the last revision:

 - remove unused imports
 - remove flaky downcall stub oome test
 - remove @throws

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16311/files
  - new: https://git.openjdk.org/jdk/pull/16311/files/6cfd8bed..52e875eb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16311&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16311&range=02-03

  Stats: 39 lines in 2 files changed: 0 ins; 39 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16311.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16311/head:pull/16311

PR: https://git.openjdk.org/jdk/pull/16311