Allow any numeric range to become a float

Currently things like `1 / 200` lead to a miscompilation because we type
`200` (and as a result, both `1` and the division result) as a ranged
number with width >= U8. During mono that forces the number to become an
`I64` because our logic was that a ranged number can only become a float
if it's at least as wide as an I8. But this is incorrect; as long as the
type is wrapped in `Frac` constructor and it's a ranged number (and not
a ranged int), it should become a fractional type.

```
» 1 / 200

0.005 : Float *
```

Closes #4047

crates/compiler/test_mono/src/tests.rs

@@ -1927,3 +1927,12 @@ fn issue_3669() {
         "#
     )
 }
+
+#[mono_test]
+fn num_width_gt_u8_layout_as_float() {
+    indoc!(
+        r#"
+        1 / 200
+        "#
+    )
+}