Treat CRLF as LF when inserting text

In effect, pasting text with \r\n will remove the \r character and
delegate whether or not the file will be saved with CRLF or LF line
endings to the `fileformat` option.

Ref #1742

internal/buffer/line_array.go

@@ -191,10 +191,15 @@ func (la *LineArray) newlineBelow(y int) {
 func (la *LineArray) insert(pos Loc, value []byte) {
 	x, y := runeToByteIndex(pos.X, la.lines[pos.Y].data), pos.Y
 	for i := 0; i < len(value); i++ {
-		if value[i] == '\n' {
+		if value[i] == '\n' || (value[i] == '\r' && i < len(value)-1 && value[i+1] == '\n') {
 			la.split(Loc{x, y})
 			x = 0
 			y++
+
+			if value[i] == '\r' {
+				i++
+			}
+
 			continue
 		}
 		la.insertByte(Loc{x, y}, value[i])