Embedded VST windows don't focus properly when clicking window content

### System Information

Windows 10

### LMMS Version(s)

1.3.0-alpha.1.942+c14a327

### Most Recent Working Version

1.2.2

### Bug Summary

Clicking on the content of an embedded VST window doesn't properly focus the window, meaning either the whole window stays behind other windows, or only the contents show on top while the titlebar and borders stay behind. Clicking the titlebar or borders focuses the window correctly, however. In 1.2.2 stable, this issue only occurs when using Qt embedding, but on the latest nightly it happens (slightly differently) with both Qt embedding and native Win32 embedding. I tested multiple VST instruments and effects and this bug happens with all of them.

This issue seems similar to the second item in #4828, however it seems that issue only occurred while using the Qt embedding mode, while this issue occurs on both the Qt and Win32 embedding modes.

### Expected Behaviour

Clicking on the content of an embedded VST window should focus it properly, like how other windows work.

### Steps To Reproduce

- Load a VST into LMMS
- Open the VST's GUI
- Drag the VST GUI window above another window within LMMS (such as the song editor)
- Click on another window within LMMS (such as the song editor)
- Click back onto the contents of the VST GUI window

### Logs

_No response_

### Screenshots / Minimum Reproducible Project

**With native Win32 API embedding:**

https://github.com/user-attachments/assets/62d8b50d-655e-412e-8fa0-63621c645287

**With Qt embedding:**

https://github.com/user-attachments/assets/a17b3868-a4d6-4db6-99e9-37b03f43f5e5

### Please search the issue tracker for existing bug reports before submitting your own.

- [x] I have searched all existing issues and confirmed that this is not a duplicate.

Reproduce the focus problem with both Qt embedding and native Win32 embedding using the listed steps, then trace the embedded VST GUI window focus handling. Done means clicking the VST content focuses the entire window, including its titlebar and borders, in both embedding modes.

Written by the indexing model from the issue text.