RFR: JDK-8286153: Remove redundant casts and other cleanup [v2]

[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`.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  address review feedback

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8543/files
  - new: https://git.openjdk.java.net/jdk/pull/8543/files/e18b0b6c..6ad78546

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8543&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8543&range=00-01

  Stats: 25 lines in 3 files changed: 3 ins; 7 del; 15 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