RFR: JDK-8286153: Remove redundant casts and other cleanup [v3]

[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:

  fix indentation

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8543/files
  - new: https://git.openjdk.java.net/jdk/pull/8543/files/6ad78546..34fd6970

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8543&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8543&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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