RFR: 8353842: C2: Add graph dumps before and after loop opts phase [v2]

[Manuel Hässig]

> This PR adds graph dumps before and after loop optimizations, but only if the compiled method actually contains loops. This helps to distinguish loop optimizations in IGV and to match loop related nodes like opaque template assertion predicates.
> 
> I tested this by compiling a few test methods and looking at the ideal graph. Also, I ran tier1 through tier3 and Oracle internal testing.

Manuel Hässig has updated the pull request incrementally with one additional commit since the last revision:

  Also print after if loops get optimized away

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24509/files
  - new: https://git.openjdk.org/jdk/pull/24509/files/b7829e0c..6fd228c4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24509&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24509&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24509.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24509/head:pull/24509

PR: https://git.openjdk.org/jdk/pull/24509