RFR: 8283094: Add Ideal transformation: x + (con - y) -> (x - y) + con

[Zhiqiang Zang]

Hello,

`x + (con - y)  -> (x - y) + con` is a widely seen pattern; however it is missing in current implementation, which prevents some obvious constant folding from happening, such as `x + (1 - y) + 2` will be not optimized at all, rather than into `x - y + 3`.

This pull request adds this transformation.

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Commit messages:
 - Merge master.
 - include transformation from (con - y) + x into (x - y) + con and x + (con - y) into (x - y) + con.

Changes: https://git.openjdk.java.net/jdk/pull/7795/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7795&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283094
  Stats: 214 lines in 4 files changed: 214 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7795.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7795/head:pull/7795

PR: https://git.openjdk.java.net/jdk/pull/7795