RFR: 8349361: C2: RShiftL should support all applicable transformations that RShiftI does [v7]

[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 one additional commit since the last revision:

  review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23438/files
  - new: https://git.openjdk.org/jdk/pull/23438/files/8bac2cab..e4053783

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23438&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23438&range=05-06

  Stats: 2 lines in 2 files changed: 1 ins; 0 del; 1 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