vfmt: change all '$expr' to '${expr}' (#16428)

examples/process/command.v

@@ -28,7 +28,7 @@ fn main() {
 	exec("bash -c 'find /tmp/'")
 	out = exec('echo to stdout')
 	out = exec('echo to stderr 1>&2')
-	println("'$out'")
+	println("'${out}'")
 	// THIS DOES NOT WORK, is error, it goes to stderror of the command I run
 	assert out == 'to stderr'
 }

examples/process/process_script.v

@@ -20,11 +20,11 @@ fn exec(path string, redirect bool) {
 	if cmd.is_alive() {
 		for {
 			line = cmd.stdout_read()
-			println('STDOUT: $line')
+			println('STDOUT: ${line}')
 
 			if !redirect {
 				line_err = cmd.stderr_read()
-				println('STDERR: $line_err')
+				println('STDERR: ${line_err}')
 			}
 
 			if !cmd.is_alive() {

examples/process/process_stdin_trick.v

@@ -17,7 +17,7 @@ fn exec(cmd string) (string, int) {
 	p.set_redirect_stdio()
 	p.run()
 
-	p.stdin_write('$cmd2 && echo **OK**')
+	p.stdin_write('${cmd2} && echo **OK**')
 	os.fd_close(p.stdio_fd[0]) // important: close stdin so cmd can end by itself
 
 	for p.is_alive() {