Use more specific type for string length

Author: GarboMuffin

src/compiler/irgen.js

@@ -344,7 +344,7 @@ class ScriptTreeGenerator {
                 right: this.descendInputOfBlock(block, 'STRING2').toType(InputType.STRING)
             });
         case 'operator_length':
-            return new IntermediateInput(InputOpcode.OP_LENGTH, InputType.NUMBER_REAL, {
+            return new IntermediateInput(InputOpcode.OP_LENGTH, InputType.NUMBER_POS_INT | InputType.NUMBER_ZERO, {
                 string: this.descendInputOfBlock(block, 'STRING').toType(InputType.STRING)
             });
         case 'operator_letter_of':

test/snapshot/__snapshots__/tw-simple-string-operations.sb3.tw-snapshot

@@ -24,7 +24,7 @@ return function funXYZ_a () {
 b0.value = "ababa";
 b1.value = "";
 b2.value = 1;
-for (var a0 = ("" + b0.value).length; a0 >= 0.5; a0--) {
+for (var a0 = ("" + b0.value).length; a0 > 0; a0--) {
 if ((((("" + b0.value))[(b2.value | 0) - 1] || "").toLowerCase() === "a".toLowerCase())) {
 b1.value = (("" + b1.value) + "b");
 } else {

test/snapshot/__snapshots__/warp-timer/tw-simple-string-operations.sb3.tw-snapshot

@@ -24,7 +24,7 @@ return function* genXYZ_a () {
 b0.value = "ababa";
 b1.value = "";
 b2.value = 1;
-for (var a0 = ("" + b0.value).length; a0 >= 0.5; a0--) {
+for (var a0 = ("" + b0.value).length; a0 > 0; a0--) {
 if ((((("" + b0.value))[((+b2.value) | 0) - 1] || "").toLowerCase() === "a".toLowerCase())) {
 b1.value = (("" + b1.value) + "b");
 } else {