RFR: 8300916: Re-examine the initialization of JNU Charset in StaticProperty [v2]

[Naoto Sato]

> This issue was found during the review of this PR: https://github.com/openjdk/jdk/pull/12132 where `Charset` class was loaded/initialized at the phase 1 of the startup process. Since `Charset` depends on `StaticProperty`, loading of `Charset` class should be delayed. I basically moved cache for `jnuCharset` into the actual calling locations `ProcessImpl` and `ProcessEnvironment` for unix platforms so that initPhase1() won't initialize `Charset` class.
> Unrelated, but I replaced `Locale.ENGLISH` with `Locale.ROOT` in the argument of `toLowerCase()`.

Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:

  Clean-up of imports

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12171/files
  - new: https://git.openjdk.org/jdk/pull/12171/files/183f5526..579aca70

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12171&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12171&range=00-01

  Stats: 8 lines in 1 file changed: 1 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/12171.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12171/head:pull/12171

PR: https://git.openjdk.org/jdk/pull/12171