improve uninitialized var tracking?

```haxe
class Test {
static function main() {
final foo = Math.random() > 0.5;
var bar;
if(foo) bar = 'bar';
for(i in 0...5) {
if(foo) trace(bar.length);
}
}
}
```
This causes `Test.hx:6: characters 16-19 : Local variable bar used without being initialized`. Could compiler figure out it's actually initialized in cases like this?
Alternatively, would some kind of metadata override make sense?

My use case is initializing the variable using inlined constructor, so initializing to null breaks the inline.

Start by reproducing the Test.hx example and its uninitialized-variable diagnostic. Investigate the compiler's tracking of bar across the if statement and the implications of the proposed metadata override, including the inline-constructor use case. Done should mean the intended initialization is accepted without requiring a null initializer, with the behavior covered by a regression test.

Written by the indexing model from the issue text.