RFR: JDK-8286153: Remove redundant casts and other cleanup

[Jonathan Gibbons]

Please review some cleanup updates to address issues reported by an IDE.

The seeds for the change were a series of redundant casts, that have now all been removed.  Various other warnings and suggestions were made by the IDE for the affected files. There were a number of places with redundant type arguments, for which the general fix was in favor of using `var` instead of `<>`.

Some `switch` statements were converted to the enhanced `switch` form, which also revealed a couple of places where `RECORD` should have been added alongside `ENUM`.

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Commit messages:
 - JDK-8286153: Remove redundant casts and other cleanup

Changes: https://git.openjdk.java.net/jdk/pull/8543/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8543&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286153
  Stats: 178 lines in 8 files changed: 4 ins; 48 del; 126 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8543.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8543/head:pull/8543

PR: https://git.openjdk.java.net/jdk/pull/8543