RFR: 8303814: getLastErrorString should avoid charset conversions [v3]

[Daniel Jeliński]

> This patch modifies the `getLastErrorString` method to return a `jstring`. Thanks to that we can avoid unnecessary back and forth conversions between Unicode and other charsets on Windows.
> 
> Other changes include:
> - the Windows implementation of `getLastErrorString` no longer checks `errno`. I verified all uses of the method and confirmed that `errno` is not used anywhere. 
> - While at it, I found and fixed a few calls to `JNU_ThrowIOExceptionWithLastError` that were done in context where `LastError` was not set.
> - jdk.hotspot.agent was modified to use `JNU_ThrowByNameWithLastError` and `JNU_ThrowByName` instead of `getLastErrorString`; the code is expected to have identical behavior.
> - zip_util was modified to return static messages instead of generated ones. The generated messages were not observed anywhere, because they were replaced by a static message in ZIP_Open, which is the only method used by other native code.
> - `getLastErrorString` is no longer exported by libjava.
> 
> Tier1-3 tests continue to pass.
> 
> No new automated regression test; testing this requires installing a language pack that cannot be displayed in the current code page.
> Tested this manually by installing Chinese language pack on English Windows 11, selecting Chinese language, then checking if the message on exception thrown by `InetAddress.getByName("nonexistent.local");` starts with `"不知道这样的主机。"` (or `"\u4e0d\u77e5\u9053\u8fd9\u6837\u7684\u4e3b\u673a\u3002"`). Without the change, the exception message started with a row of question marks.

Daniel Jeliński has updated the pull request incrementally with one additional commit since the last revision:

  Use NULL where appropriate

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12922/files
  - new: https://git.openjdk.org/jdk/pull/12922/files/ea91b651..efd72a1d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12922&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12922&range=01-02

  Stats: 12 lines in 1 file changed: 0 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/12922.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12922/head:pull/12922

PR: https://git.openjdk.org/jdk/pull/12922