Qt: Make mouse screen locking DPI aware and support render to separate window

[F0bes]

Description of Changes

When the feature was developed, I didn't think about how QWindow::geometry() might not be scaled to the current DPI.

I now scale the window geometry to the current monitors pixel scale, and then clamp.

I also made the function safer, as I was assuming a fixed size of data from GetRawInputData, and I wasn't checking if GetCursorPos was successful or not before using its result.

Also removed some unused global mouse hook stuff. Don't ever want to use that anyways.

Also implemented support for 'render to separate window'

Rationale behind Changes

Fixes #12695

Suggested Testing Steps

Test different DPIs

Did you use AI to help find, test, or implement this issue or feature?

yeah, copilot auto complete

[F0bes]

Added support for "render to separate window".

@chaoticgd tested x11 and found that one axis did not clamp properly on a non-100 DPI but I could not reproduce it here.

[F0bes]

Added support for "render to separate window".

@chaoticgd tested x11 and found that one axis did not clamp properly on a non-100 DPI but I could not reproduce it here.

The issue happens when

• You have more than one monitor
• The monitors are different resolutions
• Your DPI is not at 100%

I don't think there is much I can or want to do about that right now, so I've gone ahead and added a warning in the options description.