RFR: 8330386: Replace Opaque4Node of Initialized Assertion Predicate with new OpaqueInitializedAssertionPredicateNode [v2]

[Christian Hagedorn]

> This patch replaces the `Opaque4Node` of the `If` for Initialized Assertion Predicates with a new `OpaqueInitializedAsseritonPredicateNode`. This helps to simplify pattern matching for predicate code and to distinguish from the two other uses of `Opaque4` nodes:
> 1. Template Assertion Predicate: The goal is to get rid of its `Opaque4Node` as well by using a dedicated `TemplateAssertionPredicateNode` for the `IfNode`.
> 2. Non-null-checks with instrinsics and unsafe accesses: This will eventually be the only use left. Once we get there, we should rename the node accordingly to `OpaqueNonNullCheck` or something like that.
> 
> I went through all the uses of `Opaque4` nodes and did the following:
> - Could the `Opaque4` node be part of an Initialized Assertion Predicate?
>   - No: Added an assert that we are not dealing with an Initialized Assertion Predicate.
>   - Yes:
>     - Yes **and only** for Initialized Assertion Predicates? Added an assert that we are only expecting an `OpaqueInitializedAsseritonPredicateNode` if appropriate.
>     - Yes but could also be something else: Added case for `OpaqueInitializedAsseritonPredicateNode` next to the `Opaque4` case.
> - Is this `Opaque4` node only used for Template Assertion Predicates?
>   - Yes: Added assert with call to `assertion_predicate_has_loop_opaque_node()` to check that we find its `OpaqueLoop*Nodes`.
>  - I've added test cases where I was not sure about whether an `Opaque4` node could be part of a Template, an Initialized Assertion Predicate or a non-null-check. This was a little tricky but I think it was still worth to prevent future bugs (even though most of these special cases are quite rare).
> 
> This is another patch split off from the full fix for Assertion Predicates.
> 
> Thanks,
> Christian

Christian Hagedorn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'master' into JDK-8330386
 - Add more comments and asserts
 - Add more tests
 - 8330386: Replace Opaque4Node of Initialized Assertion Predicate with new OpaqueInitializedAssertionPredicateNode

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18951/files
  - new: https://git.openjdk.org/jdk/pull/18951/files/089a4e65..fe3feb8b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18951&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18951&range=00-01

  Stats: 22254 lines in 1611 files changed: 8283 ins; 8470 del; 5501 mod
  Patch: https://git.openjdk.org/jdk/pull/18951.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18951/head:pull/18951

PR: https://git.openjdk.org/jdk/pull/18951