RFR: 8370196: C2: Improve (U)MulHiLNode::MulHiValue [v9]

[Zihao Lin]

> If nodes both are constant, support constant folding.

Zihao Lin has updated the pull request incrementally with two additional commits since the last revision:

 - fix test failed
 - fix make unsigned

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28097/files
  - new: https://git.openjdk.org/jdk/pull/28097/files/a85229f0..6f57bcb2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28097&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28097&range=07-08

  Stats: 82 lines in 3 files changed: 24 ins; 48 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/28097.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28097/head:pull/28097

PR: https://git.openjdk.org/jdk/pull/28097