termios: new termios module (#17792)

* termio: new termio module

move the tcgetattr and tcsetattr functions in a new termio module.
The code needed refactoring as different OS have different fields
size, position and number for the C.termios structure, which
could not be correctly expressed consitently otherwise.

It has the positive side effect to reduce the number of unsafe calls.
New testing code was also added for the readline module as it is
relying of the feature.

* apply 2023 copyright to the new files too

examples/readline/correct.expect

@@ -0,0 +1,9 @@
+#!/usr/bin/expect
+spawn ./readline_ci
+send "a"
+expect "got 97"
+send "1"
+expect "got 49"
+send "q"
+expect "Goodbye."
+expect eof

examples/readline/readline.vsh

@@ -0,0 +1,2 @@
+chdir('examples/readline')!
+assert execute('./correct.expect').exit_code == 0

examples/readline/readline_ci.v

@@ -0,0 +1,29 @@
+module main
+
+import readline
+
+fn main() {
+	run() or { panic('${err}') }
+}
+
+fn run() ! {
+	$if windows {
+		eprintln('skipping test on windows for now')
+		return
+	} $else {
+		mut r := readline.Readline{}
+		r.enable_raw_mode_nosig()
+		defer {
+			r.disable_raw_mode()
+		}
+
+		for {
+			entered := r.read_char()!
+			if entered == `q` {
+				break
+			}
+			println('got ${entered}')
+		}
+		println('Goodbye.')
+	}
+}