RFR: 8230382: Clean up ConvI2L, CastII and CastLL::Ideal methods

[Emanuel Peter]

This is a cleanup job: move code from `::Ideal` methods that only change types to `::Value` where the code belongs.

`CastLLNode::Ideal` was introduced in [JDK-8229496](https://bugs.openjdk.java.net/browse/JDK-8229496) and reverted (deleted) in [JDK-8242108](https://bugs.openjdk.java.net/browse/JDK-8242108).
Currently, `CastLLNode` does not have its own `::Ideal` method. Hence, I changed nothing for it.

For `ConvI2LNode` and `CastIINode`, I went through a process of first copying the relevant code to `::Value`, calling it from `::Ideal` and asserting that they deliver equivalent results.
These intermediate code results can be found in the comments of [JDK-8230382](https://bugs.openjdk.java.net/browse/JDK-8230382).
I ran tests: final code and intermediate code versions. Ensures code behaves equivalent and nothing broke.

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

Commit messages:
 - 8230382: Clean up ConvI2L, CastII and CastLL::Ideal methods

Changes: https://git.openjdk.java.net/jdk/pull/7609/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7609&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8230382
  Stats: 158 lines in 2 files changed: 78 ins; 72 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7609.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7609/head:pull/7609

PR: https://git.openjdk.java.net/jdk/pull/7609