RFR: 8283711: Remove redundant 'new String' calls after concatenation

[Andrey Turbanov]

Result of string concatenation is a newly created String object. There is no need it wrap it in another 'new String' call.
Such calls are confusing and produce warnings in IDE. Without them code is easier to read.
Similar cleanup [JDK-8273375](https://bugs.openjdk.java.net/browse/JDK-8273375) in java.desktop

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Commit messages:
 - [PATCH] Remove redundant 'new String' calls after concatenation
 - [PATCH] Remove redundant 'new String' calls after concatenation

Changes: https://git.openjdk.java.net/jdk/pull/7876/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7876&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283711
  Stats: 13 lines in 3 files changed: 0 ins; 1 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7876.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7876/head:pull/7876

PR: https://git.openjdk.java.net/jdk/pull/7876