RFR: 8333099: Missing check for is_LoadVector in StoreNode::Identity [v2]

[Damon Fenacci]

> [JDK-8325520](https://bugs.openjdk.org/browse/JDK-8325520) introduced a check for type equality in `StoreNode::Identity` in the specific case of a load vector followed by a store vector.
> Unfortunately the memory node operand might actually not be of type `LoadVector`. So, before retrieving its type, a check for `is_LoadVector` is necessary.

Damon Fenacci has updated the pull request incrementally with three additional commits since the last revision:

 - Update test/hotspot/jtreg/compiler/vectorapi/TestIsLoadVector.java
   
   Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
 - Update test/hotspot/jtreg/compiler/vectorapi/TestIsLoadVector.java
   
   Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
 - JDK-8333099: add regression test

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19449/files
  - new: https://git.openjdk.org/jdk/pull/19449/files/9fb317a3..f4150d37

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19449&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19449&range=00-01

  Stats: 63 lines in 1 file changed: 63 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19449.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19449/head:pull/19449

PR: https://git.openjdk.org/jdk/pull/19449