This PR introduces a mechanism for passing through line rendition
attributes to the conpty client, so we can support double-width and
double-height text in Windows Terminal.

Line renditions were first implemented in conhost (with the GDI
renderer) in PR #8664, and were implemented in the DX renderer in PR
#13102.

By default this won't add any additional overhead to the conpty output,
but as soon as there is any usage of double-size text, we switch to a
mode in which every line output will be prefixed with a line rendition
sequence. This is to ensure that the line attributes in the client
terminal are always in sync with the host.

Since this does add some overhead to the conpty output, we'd prefer not
to remain in this mode longer than necessary. So whenever there is a
full repaint of the entire viewport, we check to see if all of the lines
are single-width. If that is the case, we can then safely skip the line
rendition sequences in future updates.

One other small optimization is when the conpty update is only writing
out a single character (this is something we already check for). When
that is the case, we can safely skip the line rendition prefix, because
a single character update should never include a change of the line
rendition.

## Validation Steps Performed

I've manually tested that Windows Terminal now passes the double-size
tests in _Vttest_, and also confirmed various edge cases are working
correctly in my own double-size tests.

Closes #11595