RFR: 8299513: Cleanup java.io

[Per Minborg]

Code in java.io contains many legacy constructs and semantics not recommended including: 

* C-style array declaration 
* Unnecessary visibility 
* Redundant keywords in interfaces (e.g. public, static) 
* Non-standard naming for constants 
* Javadoc typos 
* Missing final declaration 

These should be fixed as a sanity effort.

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Commit messages:
 - Cleanup ExpiringCache
 - Cleanup java.io

Changes: https://git.openjdk.org/jdk/pull/11848/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11848&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299513
  Stats: 236 lines in 25 files changed: 8 ins; 7 del; 221 mod
  Patch: https://git.openjdk.org/jdk/pull/11848.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11848/head:pull/11848

PR: https://git.openjdk.org/jdk/pull/11848