compiler,runtime: implement string to []rune conversion

Commit message by aykevl

testdata/string.go

@@ -6,6 +6,14 @@ func testRangeString() {
 	}
 }
 
+func testStringToRunes() {
+	var s = "abcü¢€𐍈°x"
+	for i,c := range []rune(s) {
+		println(i, c)
+	}
+}
+
 func main() {
 	testRangeString()
+	testStringToRunes()
 }

testdata/string.txt

@@ -7,3 +7,12 @@
 10 66376
 14 176
 16 120
+0 97
+1 98
+2 99
+3 252
+4 162
+5 8364
+6 66376
+7 176
+8 120