Complete the 8-bit interface architecture

[j4james]

Summary of the Pull Request

This PR adds support for the missing operations that are required in the
8-bit interface architecture extension.

DECAUPSS - Assign User-Preference Supplemental Set
DECRQUPSS - Request User-Preference Supplemental Set
ACS - Announce Code Structure for ANSI levels 1, 2, and 3

Detailed Description of the Pull Request / Additional comments

For the UPSS assignment there's a new wstring_view in TerminalOutput
that tracks the current mapping table for the character set, and a new
VTID field tracking the ID so it can be queried. The ANSI conformance
just required a couple of calls to existing methods to designate the
appropriate character sets and GL/GR maps.

And now that we've implemented everything that's required, I've updated
our device attributes report (DA1) to indicate support for the 8-bit
interface architecture (feature 14).

This PR also addresses some issues with the way the 8-bit GR capability
is managed. Previously a soft reset (DECSTR) would return the code
page to its startup state, and the restore cursor operation (DECRC)
could have a similar effect. This was a problem for 8-bit apps that
weren't expecting that behavior.

I've now made it so those operations no longer have any effect on the
code page, and the same applies to the C1 parsing option (DECAC1). The
only way to restore the code page and C1 parsing to their startup state
now is with a hard reset (RIS).

Validation Steps Performed

I've added unit tests covering the DECAUPSS and DECRQUPSS sequences,
and I've also manually tested their behavior in Vttest.

PR Checklist

• Closes Complete the 8-bit interface architecture #16546
• Tests added/passed

[lhecker]

Neat!

[DHowett]

Thanks so much for this! Sorry I missed this one 😄