Restore Encoding for the .NET SDK upon Exit

[nagilson]

Fixes #30170

• The encoding before the SDK is under execution is saved and then restored upon program exit. This will make it so it doesn't affect the behavior of other programs on the console. This behavior was observed before the encoding fixes for other language support, but now that the encoding is actually being applied correctly, it would occur more often.

• In addition, we have limited the build number to have the encoding UTF 8 fix only on windows builds that officially support UTF 8. Previous builds of Windows 10 2019 that were earlier, even in 2018, did have the support, but the behavior is technically unsupported and thus 'undefined.'

• Added environment variable to turn on the and force the encoding even if your OS may not support it officially, or if you don't have read registry access and so we can't tell what build of windows you're on. This is 'breaking' in the sense that previously the encoding would work for those without registry access... maybe we don't want to do that? cc @baronfel for a decision.

• This is a breaking change in that those who relied on the encoding to be changed by the SDK will no longer be able to rely on this.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[baronfel]

Added environment variable to turn on the and force the encoding even if your OS may not support it officially, or if you don't have read registry access and so we can't tell what build of windows you're on. This is 'breaking' in the sense that previously the encoding would work for those without registry access... maybe we don't want to do that? cc @baronfel for a decision.

This behavior is fine to me - we just need to make sure that the environment variable is documented.

[nagilson]

@joeloff Thanks for taking a look, I have responded to all feedback.

[nagilson]

Made a breaking change doc as well. Thanks!

[marcpopMSFT]

This should have targeted main. Preview 2 is closed and there is no automatic port to main from the preview branches. @nagilson