c2ed2e7 introduced the terminal_set_mouse_input function to various terminal
backends, but overlooked the dummy backend.
This causes linking errors when trying to build on platforms with no terminal,
as vo_kitty and vo_tct are unconditionally enabled and make use of that
function.
Removes mp_puts/mp_fputs and adds mp_fwrite.
In fact I wanted fwrite instead of puts, no need to make it more awkward
with the implicit new lines.
Fixes: fc55f355fc
In a bunch of cases, we emulate highly platform specific APIs on a
higher level across all OSes, such as IPC, terminal, subprocess
handling, and more. We have source files for each OS, and they implement
all the same mpv internal API.
Selecting which source file to use on an OS can be tricky, because there
is partially overlapping and emulated APIs (consider Cygwin on Windows).
Add a pick_first_matching_dep() function to make this slightly easier
and more structured.
Also add dummy backends in some cases, to deal with APIs not being
available.
Clarify the Windows dependency identifiers, as these are the most
confusing.
