RFR: 8300916: Re-examine the initialization of JNU Charset in StaticProperty [v5]

[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:

  Use StaticProperty.fileEncoding() & make the field @Stable

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12171/files
  - new: https://git.openjdk.org/jdk/pull/12171/files/5c37f5bc..b2268eb2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12171&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12171&range=03-04

  Stats: 7 lines in 1 file changed: 3 ins; 3 del; 1 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