Redesign new tab menu page -> dropdown

[carlos-zamora]

Summary of the Pull Request

Renames the "New tab menu" page to "Dropdown menu".
Redesigns the page with the following notes:

• the preview is now on the right side so that it's always visible
• moves preview buttons into border with previewed new tab menu entries
• when the window narrows, removes the icons from the controls, then changes layout to be vertical so that it all fits.

Aside from the main redesign changes above, a lot of the other changes are to make sure that spacing and alignment looks ok.

Validation Steps Performed

• Wide view
• Medium width view
• Narrow view

PR Checklist

Related to #17000

[carlos-zamora]

Demo

Medium size:

Narrow size:

Things to note:

• the preview aligns with the top edge of the settings controls
• the buttons for the preview were redesigned to fit in a border
• different configurations exist depending on the width of the window (see above)

[lhecker]

It's XAML.