RFR: 8349361: C2: RShiftL should support all applicable transformations that RShiftI does [v8]

[Roland Westrelin]

> This change refactors `RShiftI`/`RshiftL` `Ideal`, `Identity` and
> `Value` because the `int` and `long` versions are very similar and so
> there's no logic duplication. In the process, support for some extra
> transformations is added to `RShiftL`. I also added some new test
> cases.

Roland Westrelin has updated the pull request incrementally with two additional commits since the last revision:

 - Update src/hotspot/share/opto/mulnode.cpp
   
   Co-authored-by: Emanuel Peter <emanuel.peter at oracle.com>
 - Update src/hotspot/share/opto/mulnode.cpp
   
   Co-authored-by: Emanuel Peter <emanuel.peter at oracle.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23438/files
  - new: https://git.openjdk.org/jdk/pull/23438/files/e4053783..0f1b76ab

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23438&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23438&range=06-07

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/23438.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23438/head:pull/23438

PR: https://git.openjdk.org/jdk/pull/23438