RFR: 8373525: C2: assert(_base == Long) failed: Not a Long

[Damon Fenacci]

# Issue
Olivier's fuzzer found a test that makes C2 crash while running the optimization that collapses the addition with overflow-protection (`fold_subI_no_underflow_pattern`).

# Causes
The crash happens because during `fold_subI_no_underflow_pattern` the first input of the `AddL` node (see comment below) becomes top.
https://github.com/openjdk/jdk/blob/82b04f01bc99e8155518b8b8600d180981a42fc5/src/hotspot/share/opto/addnode.cpp#L1525-L1533

This happens because of a whole `IfFalse` subgraph that dies and nodes are being removed. `AddL` is not removed immediately as it has another input which is still alive but it is put in the IGVN worklist instead.

<img width="463" height="239" alt="image" src="https://github.com/user-attachments/assets/bce0e4b0-b823-473d-91de-2bb048841e65" />

Unfortunately the `fold_subI_no_underflow_pattern` optimization runs before the next GVN pass and triggers the assert.

# Fix
`fold_subI_no_underflow_pattern` should actually take into account that we could have the graph in such a state and that `x` could be top. So, the sensible fix is not to presume `x` to be of type long and bailout if it is not.

# Testing
Tier 1-3+
(also checked for new regression test failure before the change)

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

Commit messages:
 - JDK-8373525: add test requires
 - JDK-8373525: C2: assert(_base == Long) failed: Not a Long

Changes: https://git.openjdk.org/jdk/pull/28920/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28920&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373525
  Stats: 117 lines in 2 files changed: 116 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28920.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28920/head:pull/28920

PR: https://git.openjdk.org/jdk/pull/28920