[split-view] nested split views calculate incorrect initial sizes

[MikeMatusz]

Describe the bug:
When split views are nested, the initial sizes are incorrect.

To Reproduce:
Steps to reproduce the behavior:

1. Open the StackBlitz reproduction
2. Note that the "inner left" and "inner right" panels are supposed to each be 50%, but are clearly not the same size.
3. Note that "top" should be 40% of the available height, but is more than that.
4. Click "Adjust" to re-run private "apply size" logic and correct the sizes.

Expected behavior:
The initial sizes should be the same as the sizes after clicking "Adjust"

Screenshots:
See StackBlitz example for visuals

Please complete the following information:

• Forge version: 2.17.0
• I have searched existing issues before creating this report? Y
• Browser: All
• Platform: All
• OS: All

Additional context:

[stackblitz]

Start a new pull request in StackBlitz Codeflow.

• angular-wk4lju (Open reproduction)

[MikeMatusz]

I've also discovered that if the split-view is inside a view-switcher, switching tabs will cause panel widths to go to zero. I could potentially open a separate issue for that. Since I am specifying my widths as percentages, though, I think #388 could potentially address both of these problems for me, but unless we always want to convert pixels into percent, we may still need to address this for those cases.