Add "tabs" style for dropdown inputs

[RunDevelopment]

This adds a tab list style display for dropdowns. This style shows all options at once and allows users to quickly change between them. Just like checkboxes, tabs are implemented using preferred_style, so it's a purely visual change and doesn't affect the behavior of the input at all.

I used tabs in 3 nodes so far.

• Crop, for the Crop Mode dropdown.
• Stretch Contrast, for the Stretch Mode dropdown.
• Color From, for the Color Type dropdown.

I also renamed some enum variants to make the tabs look better. In particular, I renamed "Grayscale" to "Gray" in Color From, which makes it nicely consistent with regular color input.