RFR: 8309268: C2: "assert(in_bb(n)) failed: must be" after JDK-8306302

[Emanuel Peter]

This is the fix to a regression caused in the CMoveV fix JDK-8306302.

I had implicitly assumed that all `Cmp` in the loop also have their `in(1)` inside the loop (`in_bb`). This is not always true, and hence we hit the assert.

**Solution**

However, we know that at least one of the two inputs of a `Cmp` must also be in the loop, else the `Cmp` would float outside the loop. So if `in(1)` is not in the loop then we can just pick `in(2)` for the `velt_type`.

**Testing**
I added 2 regression tests that were provided in the bug, and also extended `TestVectorConditionalMove.java` (though it is currently problemlisted because of an IR framework bug). This extension also triggered the assert, and now properly vectorizes.

I tested up to tier6 and stress testing. I ran the tests both with `TestVectorConditionalMove` problemlisted and without the problemlisting.
**Running... but so far all good**

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

Commit messages:
 - 8309268: C2: "assert(in_bb(n)) failed: must be" after JDK-8306302

Changes: https://git.openjdk.org/jdk/pull/14268/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14268&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309268
  Stats: 135 lines in 3 files changed: 132 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/14268.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14268/head:pull/14268

PR: https://git.openjdk.org/jdk/pull/14268