[A11Y] Expose ClientSize property for forms

### Environment

VisualStudio.17.Preview/17.11.0-pre.5.0+35118.90

### .NET version

8.0

### Did this work in a previous version of Visual Studio and/or previous .NET release?

No

### Issue description

When you're blind or have very limited vision it's very hard to determine the suitable with for the form.
With the ClientSize property you can easily calculate a suitable width by adding the left and width for the right most control and adding the distance you've used for the left margin.

### Steps to reproduce

1. Create a new WinForms application and open the form.
2. Add a textbox to the form and set it's Left and Top to 12 and its width to 200.
3. Calculate the suitable form width by adding the textbox Left and Width and adding its Left once more: 12 + 200 + 12 = 224
4. Set the form width to 224.

Not quite right.

### Diagnostics

_No response_