RFR: JDK-8309266: C2: assert(final_con == (jlong)final_int) failed: final value should be integer

[Eric Nothum]

**Acknowledgments**: Thanks to @quadhier for the preliminary work on this issue: https://github.com/openjdk/jdk/pull/14353

**JDK-8309266**: TestLoopLimitOverflowDuringCCP.java causes an assertion error (overflow check) in LoopLimitNode::Value. To fix the issue I added a check in LoopLimitNode::Value that verifies that the input nodes are ConI type nodes. 

Previously, TestLoopLimitOverflowDuringCCP would cause the assertion error in LoopLimitNode::Value, during PhaseCCP::analyze. The problem originated from PhaseCCP initializing all types to TOP, resulting in the Phi node from `int limit = flag ? 1000 : Integer.MAX_VALUE` being temporarily considered as Integer.MAX_VALUE. This happens as the Node for the Integer.MAX_VALUE case was already analyzed by CCP while the Node for the 1000 case was still initialized to TOP. When resolving the value of the Phi node, Integer.MAX_VALUE and TOP get merged to Integer.MAX_VALUE, which is then processed by LoopLimitNode::Value as a constant, resulting in the integer overflow.

By checking that the input nodes are ConI nodes in LoopLimitNode::Value, we avoid Phi nodes being misinterpreted during PhaseCCP. If the Phi nodes turn out to be constant they should rather be first transformed to ConI nodes.

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

Commit messages:
 -  JDK-8309266: Cosmetic change to the if statement
 -  JDK-8309266: 1) Added TestLoopLimitOverflowDuringCCP to the jtreg tests 2) Verify in LoopLimitNode::Value that the input nodes are ConI type nodes.

Changes: https://git.openjdk.org/jdk/pull/14490/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14490&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309266
  Stats: 59 lines in 2 files changed: 55 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/14490.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14490/head:pull/14490

PR: https://git.openjdk.org/jdk/pull/14490