Allow ANCM in-process to interpret request headers as Latin1 encoded

Similar issue with Kestrel: https://github.com/dotnet/aspnetcore/issues/17399

Related PR for the fix in Kestrel: https://github.com/dotnet/aspnetcore/pull/18255

This is a very similar ask that we had for Latin1 support in Kestrel.

In a 3.1 patch we should provide:

• A config setting to change the default encoding to Latin1
• When enabled, ANCM will widen each incoming byte to a UTF-16 character and build a string from that set of characters, instead of interpreting bytes as UTF-8.
• We will continue to reject control characters from the ASCII set (0x00-0x1F and 0x7F), but not reject control characters from the widened Latin1 set (because they would collide with other interpretations of this data, like UTF-8).

This would allow a consumer to reinterpret the data in this string as a UTF-8 sequence if desired.

In 5.0 we’ll look at broader work to improve this experience. The 3.1 goals are scoped down to specific requests we’ve received.

[jkotalik]

Costing as medium though as things always take longer than expected 😄

[Pilchie]

Yes, sounds good. Thanks @jkotalik.