RFR: 8297519: Improve expressions and modernise code

[Per Minborg]

During the work of another PR (https://github.com/openjdk/jdk/pull/11260), several improvement areas were identified. These are now adressed in this separate PR proposing the use of more modern Java constructs as well as simplifying a large number of logical expressions that were previously non-normative. 


This branch has been tested and passed tier1-4 tests.

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Commit messages:
 - Modernise classes

Changes: https://git.openjdk.org/jdk/pull/11348/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11348&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297519
  Stats: 1138 lines in 31 files changed: 163 ins; 363 del; 612 mod
  Patch: https://git.openjdk.org/jdk/pull/11348.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11348/head:pull/11348

PR: https://git.openjdk.org/jdk/pull/11348