[lworld] RFR: 8275220: [lworld] Various compiler code cleanups and refactoring [v2]

[Tobias Hartmann]

> This patch contains various code cleanups, refactorings and small improvements that I cherry-picked from the nullable Q-types prototype work.
> 
> Thanks,
> Tobias

Tobias Hartmann has updated the pull request incrementally with one additional commit since the last revision:

  Restore accidentally deleted code

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

Changes:
  - all: https://git.openjdk.java.net/valhalla/pull/561/files
  - new: https://git.openjdk.java.net/valhalla/pull/561/files/7f3a3266..b1b70765

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=valhalla&pr=561&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=valhalla&pr=561&range=00-01

  Stats: 14 lines in 1 file changed: 8 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/561.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/561/head:pull/561

PR: https://git.openjdk.java.net/valhalla/pull/561