Fix #7295, #4513

Replaces tty_rows()/tty_cols() with tty_size(), which calls
uv_tty_get_winsize() to get the terminal size
Make size(UnixTerminal) return a tuple
Remove try from tty_size()

I realized that the REPL uses size without try, so if it might fail on
a normal system would probably already know about it.
Move FakeTerminal to test/repl.jl
Add deprecation warnings for tty_rows() and tty_cols()

These were never exported, but there are a decent number of packages
that use them.
Merge pull request #7297 from JuliaLang/sjk/tty_size

RFC: Use real terminal size for show (fix #7295 and #4513)