Replace mattn/isatty and containerd/console with golang.org/x/term.
This mostly affects Windows. On Windows, unlike Unix, the console (TTY)
has different handles for input/output. Using the Console API, we need
to enable VT input on the input handle (CONIN) and VT processing on the
output handle (CONOUT). Doing so enables processing VT sequences on
Windows i.e. ANSI colors, mouse sequences, cursor movements, etc.
We already handle enabling VT processing for the program output using
Termenv `EnableVirtualTerminalProcessing`. For the input side, we enable
VT input right before setting the console to raw.
By doing this, we can drop both containerd/console and mattn/isatty.
This commit also contains some refactors:
* Refactor away inputStatus type
* Refactor away program.inputIsTTY member
* Simplify how we setup and restore input when it's a TTY