avm2: Fix getChildByName to be case sensitive (close #19765)

Author: MrCheeze

core/src/avm2/globals/flash/display/display_object_container.rs

@@ -169,7 +169,7 @@ pub fn get_child_by_name<'gc>(
         .and_then(|this| this.as_container())
     {
         let name = args.get_string(activation, 0)?;
-        if let Some(child) = dobj.child_by_name(&name, false) {
+        if let Some(child) = dobj.child_by_name(&name, true) {
             return Ok(child.object2());
         } else {
             return Ok(Value::Null);

tests/tests/swfs/avm2/displayobjectcontainer_getchildbyname_wrongcase/output.txt

@@ -0,0 +1,5 @@
+//this.getChildByName("child_CLIP")
+null
+//this.addChild(newChild)
+//this.getChildByName("new_CHILD")
+null

tests/tests/swfs/avm2/displayobjectcontainer_getchildbyname_wrongcase/test.swf

@@ -0,0 +1 @@
+num_frames = 1