RFR: 8338897: Small startup regression remains after JDK-8309622 and JDK-8331932 [v2]

[Claes Redestad]

> #14404 caused some startup regressions, where the main cause of startup increase in that change was due the use of - and the not very optimized state of - runtime bootstrapped switches. This was remedied by a series of optimizations to the switch bootstrap methods and finally a desugaring of the switch added by #14404. Now @shipilev reports that there appears to be some lingering startup issue from #14404. 
> 
> One thing that stands out is a couple of caches which are being eagerly initialized regardless of user locale. This PR makes those caches lazily initialized and slightly more efficient (no need to implement `UnaryOperator` after inlining some code). Avoids loading 4 classes if running the HelloStream startup test in a locale that's in the set of constant base locales, 2 otherwise. This doesn't really do much to move the needle for startup on my setup, but tentatively it's the only remaining inefficiency I've found that came from #14404.

Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:

  final

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20713/files
  - new: https://git.openjdk.org/jdk/pull/20713/files/791a3c39..b87da2d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20713&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20713&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20713.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20713/head:pull/20713

PR: https://git.openjdk.org/jdk/pull/20713