RFR: 8336919: Cleanup and rename tags in placeholders code

[Coleen Phillimore]

This change does some renaming of tags, fields and function name (resolve_super_or_fail => resolve_with_circularity_detection) in the Placeholders and SystemDictionary (class loading) code.  resolve_super_or_fail implied that it's always the super class, which it is not, especially with the upcoming changes to valhalla.  Renaming the function to resolve/load and check for circularity error is more accurate. These are changes made by @fparain brought over from the valhalla branch.
Tested with tier1-4.

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Commit messages:
 - reword assert message.
 - A few more renames and some minor reformatting.
 - Rename resolve_with_circularity_detection to remove or_fail because it's implicit in the name.
 - Remove valhalla-only comment
 - 8336919: Cleanup and rename tags in placeholders code

Changes: https://git.openjdk.org/jdk/pull/20279/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20279&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336919
  Stats: 82 lines in 6 files changed: 3 ins; 0 del; 79 mod
  Patch: https://git.openjdk.org/jdk/pull/20279.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20279/head:pull/20279

PR: https://git.openjdk.org/jdk/pull/20279