RFR: 8356893: Use "stdin.encoding" for reading System.in with InputStreamReader/Scanner

[Roger Riggs]

On Wed, 21 May 2025 20:56:31 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

> There are several locations in the JDK source where `System.in` and `FileDescriptor.in` is read with `InputStreamReader` and `Scanner` using the default charset. As recommended by the recently merged [JDK-8356420](https://bugs.openjdk.org/browse/JDK-8356420), this PR replaces the default charset with the one provided by the `stdin.encoding` system property.
> 
> ### Fixing strategy
> 
> * Where it is obvious that `System.in` is passed to `InputStreamReader`/`Scanner` ctors, `stdin.encoding` is employed fixed.
> * Where the `InputStream` passed to `InputStreamReader`/`Scanner` ctors is difficult to determine if it can ever be `System.in`, `assert` expressions are placed.
> * Where the odds of receiving `System.in` are low, yet it is technically possible (e.g., `Process::getInputStream`, `URL::openConnection`, `Class::getResourceAsStream`), nothing is done.
> 
> @naotoj was kind enough to guide me in this PR, and stated `assert` expressions can be skipped, since they are many ways one can circumvent those checks; wrapping `System.in`, usage of `System::setIn`, etc. Yet we decided to leave them as is to collect feedback from other reviewers too.
> 
> ### Scanning strategy
> 
> The following ~alien technology~ advanced static analysis tools are used to scan the code for potentially affected places:
> 
> 
> # Perl is used for multi-line matching
> find . -name "*.java" -exec perl -0777 -ne 'my $r = (/(InputStreamReader|Scanner)(\s*System.in)/) ? 0 : 1; exit $r' {} ; -print
> git grep -H 'FileDescriptor.in' "*.java"
> 
> 
> All calls to `InputStreamReader::new` and `Scanner::new` are checked too.
> 
> ### Problems encountered
> 
> 1. Due to either irregular, or non-existent license header, could not update the copyright year for following classes:
> 
>     ```
>     DOMImplementationRegistry 
>     InputRC 
>     ListingErrorHandler 
>     PandocFilter 
>     ```
> 2. Could not employ `stdin.encoding` in `PandocFilter`, since the bootstrap VM running that class returns empty for that system property

There too many changes in too many different areas to be in a single PR.
Please break it down by review areas.  Client, core libs, tools, etc.

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PR Review: https://git.openjdk.org/jdk/pull/25368#pullrequestreview-2859185030