vrepl: add support for Home and End keys (#16116)

vlib/term/utf8.v

@@ -0,0 +1,54 @@
+module term
+
+// utf8_getchar returns an utf8 rune from standard input
+pub fn utf8_getchar() ?rune {
+	c := getchar()
+	if c == C.EOF {
+		return none
+	}
+	len := utf8_len(u8(~c))
+	if c < 0 {
+		return 0
+	} else if len == 0 {
+		return c
+	} else if len == 1 {
+		return -1
+	} else {
+		mut uc := c & ((1 << (7 - len)) - 1)
+		for i := 0; i + 1 < len; i++ {
+			c2 := getchar()
+			if c2 != -1 && (c2 >> 6) == 2 {
+				uc <<= 6
+				uc |= (c2 & 63)
+			} else if c2 == -1 {
+				return 0
+			} else {
+				return -1
+			}
+		}
+		return uc
+	}
+}
+
+// utf8_len calculates the length of a utf8 rune to read, according to its first byte
+pub fn utf8_len(c u8) int {
+	mut b := 0
+	mut x := c
+	if (x & 240) != 0 {
+		// 0xF0
+		x >>= 4
+	} else {
+		b += 4
+	}
+	if (x & 12) != 0 {
+		// 0x0C
+		x >>= 2
+	} else {
+		b += 2
+	}
+	if (x & 2) == 0 {
+		// 0x02
+		b++
+	}
+	return b
+}