We need to force the codepage to UTF8 this to avoid having our UTF-8
bytestreams be misinterpreted, and to restore the original before we're
done.
refs: https://github.com/wez/wezterm/issues/1435
implement missing alt-screen support and fixup building the examples
while we're in here.
refs: #1244
It's been replaced with an opaque termwiz error type instead.
This is a bit of a more conservative approach than that in (refs: #407)
and has less of an impact on the surrounding code, which appeals to
me from a maintenance perspective.
refs: #406
refs: #407
