RFR: 8319532: jshell - Non-sealed declarations sometimes break a snippet evaluation

[Jan Lahoda]

JShell does not understand "non-sealed" modifier when splitting input into snippets. The reason is that `CompletenessAnalyzer.parseDeclaration` (https://github.com/openjdk/jdk/blob/cdf337357a62dd52c00e56e75912565e15b6adfd/src/jdk.jshell/share/classes/jdk/jshell/CompletenessAnalyzer.java#L687) is skipping through the declaration's initial tokens, but does not know it should ignore the `-` in the `non-sealed`. This patch fixes that by making `-` part of the declaration.

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Commit messages:
 - Cleanup.
 - 8319532: jshell - Non-sealed declarations sometimes break a snippet evaluation

Changes: https://git.openjdk.org/jdk/pull/16523/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16523&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319532
  Stats: 10 lines in 2 files changed: 7 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16523.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16523/head:pull/16523

PR: https://git.openjdk.org/jdk/pull/16523