RFR: 8281505: Add CompileCommand PrintIdealPhase

[Nils Eliasson]

1. This patch adds the CompileCommand PrintIdealPhase. It allows to specify a list of compiler phases that will print the ideal IR.

-XX:CompileCommand=PrintIdealPhase,Class::method,MATCHING,FINAL_CODE"

The motivation for this is that during work with the IR framework I have found the need for printing specific phases, and the previously added PrintIdealLevel is forced to use levels that just prints to much. (I will remove PrintIdealLevel in a separate patch since it's not needed anymore.)

I have chosen not to add PrintIdealPhase as a VM flag, but keep it as CompileCommand/CompilerControl only.

2. This patch also changes the print_ideal output to emit the start tag with the phase name instead of the description, so that the name in the CompileCommand matches with what ends up in the tag. That tag is a new addition since PrintIdealLevel, so no one is using it yet.

3. This patch also removes an unused allocation in register_jfr_phasetype_serializer. 

Please review,
Nils Eliasson

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Commit messages:
 - Fix checks
 - Add validator check
 - Add Test
 - Fix product build
 - PrintIdealPhase

Changes: https://git.openjdk.java.net/jdk/pull/7392/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7392&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281505
  Stats: 407 lines in 10 files changed: 305 ins; 31 del; 71 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7392.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7392/head:pull/7392

PR: https://git.openjdk.java.net/jdk/pull/7392