Add missing flags in theme.json

[oandregal]

To be merged alongside #1967

This PR does the following:

Add flag appearanceTools.

• It was part of theme.json: add appearanceTools flag to opt-in into appearance UI controls gutenberg#36646 that is being backported at Update @wordpress packages #1967 but the theme.json changes are missing.

Add flags defaultPalette and defaultGradients.

• They were part of Color UI component: reorder palettes and update names (core by defaults, user by custom) gutenberg#36622 that was backported at Update @wordpress packages #1928 but the theme.json changes were missed.

Sort keys alphabetically so it's easier to compare this with Gutenberg.

• Related Gutenberg PR theme.json: sort keys alphabetically gutenberg#36968

[noisysocks]

Thanks @oandregal. I'll merge this into #1967.