fix: JS random int block with non-ints.

Previously random_int(2.4, 2.6) would return 2.  This is wrong.  NaN is better; it's the same as random_int("hello", []).

Python, Lua, PHP all have their own native functions for random int, so we just use their native behaviours.  Dart is another matter (separate PR).

I think making this block more accurate is worth the code given that a LOT of kids use "random integer" for stuff.

Also re-flow the Math test blocks, they were overlapping.
And the Dart interpreter link has changed URLs.

generators/javascript/math.ts

@@ -414,12 +414,20 @@ export function math_random_int(
     'mathRandomInt',
     `
 function ${generator.FUNCTION_NAME_PLACEHOLDER_}(a, b) {
+  a = Number(a);
+  b = Number(b);
   if (a > b) {
     // Swap a and b to ensure a is smaller.
     var c = a;
     a = b;
     b = c;
   }
+  a = Math.ceil(a);
+  b = Math.floor(b);
+  if (a > b) {
+    // No integers between the inputs (e.g. 2.4 & 2.6).
+    return NaN;
+  }
   return Math.floor(Math.random() * (b - a + 1) + a);
 }
 `,