RFR: 8283094: Add Ideal transformation: x + (con - y) -> (x - y) + con [v5]

[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.

Zhiqiang Zang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:

 - Merge master.
 - rename test cases.
 - move tests to existing test classes.
 - comment out "x+(0-y)" -> "(x-y)" and "(0-y)+x" -> "(x-y)" because they
   are covered already.
 - Merge master.
 - include transformation from (con - y) + x into (x - y) + con and x + (con - y) into (x - y) + con.

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Changes: https://git.openjdk.java.net/jdk/pull/7795/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7795&range=04
  Stats: 133 lines in 5 files changed: 105 ins; 0 del; 28 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