RFR: 8354464: Additional cleanup setting up native.encoding [v2]

[Stuart Marks]

> Remove the #ifdef MACOSX from platform-independent System.c, which (on Mac) sets native.encoding from sprops.encoding or (on non-Mac Unix and Windows) sets native.encoding from sprops.sun_jnu_encoding. After this removal, the native.encoding property will be set from sprops.encoding and the sun.jnu.encoding property will be set from sprops.sun_jnu_encoding.
> 
> Change the windows java_props_md.c so that it initializes sprops.sun_jnu_encoding and then copies that value to sprops.encoding. Previously, sprops.encoding was initialized with data from other Windows APIs, but this value was ignored by platform-independent code, which was kind of confusing.
> 
> There are no changes to the Unix (Mac & non-Mac) platform-specific code. It already has code to set sprops.encoding and sprops.sun_jnu_encoding properly, including macOS-specific code to set the latter to UTF-8 unconditionally.
> 
> There should be no behavior changes on any platform.
> 
> I changed variable names in windows/java_props_md.c to make it clear that the values stored into them are unused. Of course there are other possibilities here, such as changing the interface to SetupI18nProps(). I'm open to suggestions.

Stuart Marks has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Move asserts into platform-independent code.
 - Merge branch 'master' into JDK-8354464-additional-cleanup-native-encoding
 - Rename variables to make clear they're not used.
 - 8354464: Additional cleanup setting up native.encoding

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/24607/files
  - new: https://git.openjdk.org/jdk/pull/24607/files/328fdd27..37cd3ed2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24607&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24607&range=00-01

  Stats: 175846 lines in 316 files changed: 7409 ins; 167532 del; 905 mod
  Patch: https://git.openjdk.org/jdk/pull/24607.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24607/head:pull/24607

PR: https://git.openjdk.org/jdk/pull/24607