RFR: 8263448: CTW: fatal error: meet not symmetric

[Vladimir Kozlov]

In bug's case instance_id should be changed to InstanceBot only if it is real id and not InstanceTop or InstanceBot (similar to Constant in type lattice). Otherwise we incorrectly change InstanceTop to InstanceBot.  In short, we should follow PTR transformation in this code:
      if (ptr == Constant) {
         ptr = NotNull;
      }
-     instance_id = InstanceBot;
+     if (instance_id > 0) {
+       instance_id = InstanceBot;
+     }
I noticed that `TypeInstPtr::xmeet_helper()` has the same code as `TypeAryPtr::xmeet_helper()` for case when `InstPtr` meets `AryPtr`. So instead of fixing two places I decided to call TypeAryPtr::xmeet_helper() from `TypeInstPtr::xmeet_helper()` for this case. We do similar thing in `TypeOopPtr::xmeet()`:
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/type.cpp#L3283

Fixed code style in touched code.

Tested failing test from bug report, hs-tier1-4, hs-comp.

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Commit messages:
 - 8263448: CTW: fatal error: meet not symmetric

Changes: https://git.openjdk.java.net/jdk/pull/3298/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3298&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263448
  Stats: 67 lines in 1 file changed: 9 ins; 42 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3298.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3298/head:pull/3298

PR: https://git.openjdk.java.net/jdk/pull/3298